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Wiring diagram showing how to wire a thermostatic cooling fan switch to the MASTERCELL NGX in the Infinitybox IPM1 KitCopyright 2026 Infinitybox, LLC. All Rights Reserved.

Wiring the Cooling Fan with the IPM1 Kit

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Table of Contents

Overview

Your Infinitybox IPM1 Kit makes it easy to control your cooling fan. The MASTERCELL NGX takes the trigger signal from your temperature switch or ECU. It sends a command over the CAN network to the front POWERCELL to turn the cooling fan on and off. The POWERCELL has the switching and fuse protection built in. This eliminates the need for an external relay and a separate fuse for your cooling fan circuit.

The POWERCELL also soft-starts the cooling fan motor. This reduces the in-rush current when the fan first turns on. Soft-starting lets you drive a larger fan with a smaller gauge of wire. Click here to learn more about the benefits of soft-starting.

There are two main ways to trigger your cooling fan with the MASTERCELL NGX. You can use a traditional thermostatic switch or you can use the trigger from your ECU. The MASTERCELL NGX accepts both ground-switched and high-side switched (12-volt) inputs. This gives you the flexibility to handle either type of trigger without adding external components.

Before you go any further, check the configuration sheet that came with your IPM1 Kit. Your configuration sheet is the single point of truth for the wire colors and connector locations in your system. It will tell you which MASTERCELL NGX input is assigned to your cooling fan and which POWERCELL output drives the fan motor.

Wiring a Thermostatic Switch

The most common way to trigger your cooling fan is with a thermostatic switch. This is a temperature-activated switch that is usually threaded into your radiator or your engine. Inside the switch, there is a bi-metal element that is set for a specific temperature. When the coolant temperature exceeds that set point, the switch closes internally and connects its terminal to ground. When the coolant temperature drops below the set point, the switch opens and disconnects from ground.

This is a ground-switched signal. You are going to connect the MASTERCELL NGX input for your cooling fan directly to the terminal on the thermostatic switch. When the switch closes, it will ground the MASTERCELL NGX input. The MASTERCELL NGX sees this change and sends a command to the front POWERCELL to turn on the cooling fan output. When the switch opens, the MASTERCELL NGX sends a command to turn the output off.

There are two common types of thermostatic switches. The most common type has a single quick-disconnect terminal. This type of switch grounds through its metal body when it threads into the radiator or the engine. You connect the MASTERCELL NGX input wire to that terminal.

The second type has two terminals. Both terminals are isolated from the metal body of the switch. You connect the MASTERCELL NGX input to one terminal and connect the other terminal to ground.

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Here is an important note about temperature switches and temperature senders. There is a big difference between them. A temperature switch turns on and off at a set temperature. A temperature sender is a variable-resistance device that controls your temperature gauge. You cannot connect your cooling fan input on the MASTERCELL NGX to your temperature sender. They are two separate devices with two separate functions.

Wiring the Cooling Fan Trigger from an ECU

Many modern ECUs and EFI systems have a dedicated output to trigger the cooling fan. The ECU monitors the engine coolant temperature through its own sensor and decides when to turn the fan on and off. If your ECU has this capability, you can wire its cooling fan trigger directly to the MASTERCELL NGX instead of using a thermostatic switch.

The important thing to understand is whether your ECU has a ground-switched trigger or a 12-volt (high-side switched) trigger. Check the manual for your ECU to determine which type of trigger it has. The MASTERCELL NGX can handle both types of triggers natively.

Wiring diagram showing how to wire a thermostatic cooling fan switch to the MASTERCELL NGX in the Infinitybox IPM1 Kit

This diagram shows the connections between the thermostatic cooling fan switch, the MASTERCELL NGX, and the front POWERCELL in the Infinitybox IPM1 Kit.

Ground-Switched Trigger from ECU

If your ECU has a ground-switched cooling fan trigger, it internally connects the trigger wire to ground when it wants the fan on. You are going to connect this trigger to a ground-switched input on the MASTERCELL NGX.

We always recommend isolating any ground-switched input from an external system like an ECU with a 1N4001 diode. The reason is that we do not know what the ECU does with its trigger when it is off. It may let the trigger voltage float or it may pull the trigger up to battery voltage. Either of these conditions could cause erratic behavior on the MASTERCELL NGX input. To isolate the input, solder a 1N4001 diode in series between the MASTERCELL NGX input and the cooling fan trigger wire on the ECU. Install the diode with the anode facing the MASTERCELL NGX. The orientation of this diode is critical and the system will not work correctly if the diode is wired backwards.

12-Volt Trigger from ECU

If your ECU has a 12-volt cooling fan trigger, it outputs battery voltage on the trigger wire when it wants the fan on. You are going to connect this trigger to one of the high-side switched inputs on the MASTERCELL NGX.

The MASTERCELL NGX has the ability to accept 12-volt input signals directly on its high-side switched inputs. There is no need for an inVERT Mini or any other external component to flip this signal. This is one of the key advantages of the MASTERCELL NGX in your IPM1 Kit.

Adding a Bypass Switch

You may want to add a bypass switch that lets you turn on the cooling fan manually at any time. This is usually a simple toggle switch on the dash. It gives you the ability to turn the fan on even when the engine is not up to temperature.

To wire a bypass switch, connect a MASTERCELL NGX ground-switched input to one terminal on the toggle switch. Connect the other terminal to ground. You can assign this to the same cooling fan output on the POWERCELL through your inCODE NGX configuration. When you flip the switch, it grounds the MASTERCELL NGX input and turns on the cooling fan regardless of the state of your thermostatic switch or ECU trigger.

Check your configuration sheet for the specific input assigned to your bypass switch.

Wiring the POWERCELL Output to the Cooling Fan

Once you have the trigger side wired to the MASTERCELL NGX, you need to wire the output side. Connect the cooling fan output on your front POWERCELL to one wire on the cooling fan motor. Connect the other wire on the cooling fan motor to a good chassis ground. Make sure you have a solid metal-to-metal connection with no paint, grease, powder coating, or dirt in the way.

We recommend using a 25-amp fuse in the POWERCELL output to protect the wiring between the POWERCELL and the fan motor. Check your configuration sheet for the specific output and wire color for your cooling fan.

Resources

Our resources section has wiring diagrams for many different ECU and EFI systems. These show the specific connections between the ECU and the MASTERCELL NGX for the cooling fan trigger, fuel pump trigger, and ignition power. Check the blog on our website for your specific ECU.

Click here to contact our team or call us at (847) 232-1991 with any questions about wiring your cooling fan with the IPM1 Kit.

Picture of Holley HP EFIImage used courtesy of Holley Performance Products, Inc.

Wiring the Holley HP EFI System

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This blog post goes through the details of wiring the Holley HP EFI System with our Infinitybox 20-Circuit Kit.  We will show you the ease and simplicity of wiring your EFI system with Infinitybox.  The wiring is simple and short and you can eliminate the need for external relays.  We’ll go through the key steps and give you a wiring diagram that shows you all the details to wire your Holley HP EFI Engine Management System with our Infinitybox system.

Before we get too far, you must thoroughly read and understand the instructions that came from Holley to install the HP EFI system.  Please consult their website to get the instillation instructions.  The other important thing to consider here is that we are going to show you how to connect your Infinitybox wiring system to the Holley HP.  This will include wiring the key-on ignition power, the cooling fan trigger and the fuel pump trigger.  Consult the Holley manual for all details regarding primary power from the battery, coil wiring, injector wiring, sensor wiring and grounds.  This diagram shows you the connections between your Infinitybox system and the Holley HP ECU.

Picture of wiring diagram showing how to wire Holley HP EFI system with the Infinitybox wiring system

Picture of wiring diagram showing how to wire Holley HP EFI system with the Infinitybox wiring system

Your Infinitybox 20-Circuit Kit powers the key electrical systems in your car.  We’re going to provide the key-on ignition power to the Holley HP system.  You are going to connect your POWERCELL ignition output to the 12V Switched wire in the Holley Harness.  This is their Red/White wire.  In most Infinitybox configurations, your ignition output is the light-green wire on your front POWERCELL but we encourage you to always use your configuration sheet to confirm wire colors in your specific kit.  You can get more details on your configuration sheet by clicking this link.  When you turn on your ignition switch, the POWERCELL will provide the key-on ignition power that the Holley HP needs to run.  You can learn more about wiring your ignition switch to your MASTERCELL by clicking this link.

You can use an output your Infinitybox rear POWERCELL to provide the power to your fuel pump.  There are several advantages to using the fuel pump output on your POWERCELL.  First, you do not need to use a relay.  The POWERCELL has the capability to control 25-amps to your fuel pump directly without a relay.  The second advantage is that you can power the fuel pump from the POWERCELL in the back of your car.  This keeps your wiring short and easy to install.  The Holley HP ECU has a fuel pump trigger that you can connect into the MASTERCELL input for your fuel pump.  The Holley fuel pump signal is +12 volts so you must use one of our inVERT Minis to flip this to a ground trigger to go into the MASTERCELL.  You can learn more about the inVERT Mini at this link.

You can also use an output on your Infinitybox front POWERCELL to power your cooling fan.  You get same benefits with your cooling fan as you do your fuel pump.  Your wiring is shorter and you do not need to use an external relay to control the fan.  You can either use a thermostatic switch on the engine or you can have the Holley HP ECU send the MASTERCELL the signal to control the fan.  This link will show you how wire in a thermostatic switch.  The Holley HP ECU has programmable outputs that can be used to signal the MASTERCELL input for the cooling fan.  You need to use one of their “G” or ground switched outputs and need to configure this within their software tool.  You must use a diode to isolate the output on the Holley HP from the MASTERCELL.  See the details in our wiring diagram.

Those are all of the connections that you need to make between your Infinitybox 20-Circuit Kit and the Holley HP EFI system.  You can download a PDF of this wiring diagram by clicking this link.

Click on this link to contact our technical support team if you have any questions about wiring your Holley HP EFI system with Infinitybox.

The Dakota Digital PAC-2800BT

Dakota Digital PAC-2800BT Cooling Fan Controller

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This blog post is going to show you how to use the Dakota Digital PAC-2800BT to control your cooling fan with the Infinitybox system.  The PAC-2800BT is a powerful controller that lets you program the temperatures that turn on and turn off your cooling fans.  You have the flexibility to use any temperature sender, take in OBDII data from a modern ECU, even interface with the VHX & RTX gauges.  We’ve blogged before about wiring the VHX and RTX gauges with the Infinitybox system.  Click on the links to learn more.

There are multiple advantages to using the Infinitybox system with the Dakota Digital PAC-2800BT controller.  First, you can eliminate the external relay and the fuse.  These are built into the POWERCELL.  Next, you can streamline your wiring.  The PAC-2800BT would be located behind your dash, near the MASTERCELL.  The power for the fans comes from the front POWERCELL, which is located strategically where you need it in the car.  Lastly, the POWERCELL has the ability to soft-start the cooling fan.  This decreases the in-rush current to the fan and lets you drive a larger fan with a smaller gauge of wire.  You can read more about this at this link.

As always, we strongly encourage you to read and understand the manuals for anything that you are installing in your car.  Dakota Digital has a very detailed manual for the PAC-2800BT.  You can access it by clicking this link.  Also, this blog post is going to cover the wiring between the Infinitybox system and the PAC-2800BT.  This includes ignition power, the cooling fan triggers to the MASTERCELL and the cooling fan output from the POWERCELL.  Follow the Dakota Digital instructions for wiring battery power, ground, the temperature sender and the other optional features of the PAC-2800BT.

The following picture shows the connections between the Infinitybox MASTERCELL and the POWERCELL for the PAC-2800BT.

Picture of a wiring diagram showing how to wire the Dakota Digital PAC-2800 BT with the Infinitybox 20-Circuit Kit

Picture of a wiring diagram showing how to wire the Dakota Digital PAC-2800 BT with the Infinitybox 20-Circuit Kit

First, you need to get ignition or key-on  power to the PAC-2800BT.  This is going to come from the POWERCELL output for the ignition.  This is output 3, the light-green wire on the front POWERCELL in most systems, .  Please check your specific configuration sheet to confirm.  You can going to bring this ignition power to the IGNITION terminal on the PAC-2800BT module.  You are going to tap off your POWERCELL ignition output to get this power.  You can splice into this wire or you can use our Splice Saver kit to create an ignition junction point.

Next, you are going to connect your MASTERCELL cooling fan inputs to the triggers on the PAC-2800BT.  In most systems, your cooling fan is input 10, which is the blue wire with the green tracer.  Check your configuration sheet to confirm.  If you are using only one cooling fan, Dakota Digital tells you to use the FAN LOW terminal on the PAC-2800BT.  We strongly recommend that you install a diode in-line between the MASTERCELL and the PAC-2800BT.  This should be a 1N4001 diode that can be purchased easily from Amazon.  The orientation of this diode is critical and the system will not work correctly if it is wired backwards.  The diode lead on the side with the stripe should be connected to the PAC-2800BT.

Lastly, you are going to connect your POWERCELL output for the cooling fan to the wires on the fan motor.  The other wire on the fan motor should be connected to a good chassis ground.   This link will get you more details on wiring the cooling fan with the POWERCELL output.

The PAC-2800BT gives you the option to control two separate cooling fans.  If you want to use a second cooling fan, you would simply repeat wiring an unused MASTERCELL input to the PAC-2800BT and an OPEN POWERCELL output to your second cooling fan.  In most of our kits, output 8 on the front POWERCELL can be used as an auxiliary output.  You can use this one to power your second cooling fan.  See your specific configuration sheet for more details.

Here is how all of this works.  The PAC-2800BT takes in the temperature data from the temperature sender, the Dakota Digital gauge controller or the ECU via OBDII.  If the temperature it reads goes higher than the value that you programmed in it, it grounds the MASTERCELL input for the cooling fan.  This turns on the cooling fan input.  The MASTERCELL sends a command to the POWERCELL in the front of the car to turn on the output for the cooling fan.  When the temperature drops below the set point that you programmed in the PAC-2800BT, it turns off the MASTERCELL input for the cooling fan.  The MASTERCELL sends a command to the front POWERCELL to turn off the fan.  It is that easy.

If you choose the option to use two cooling fans, the PAC-2800BT will manage both fans together to control the engine temperature.

There is a PDF copy of this wiring diagram available on our website.  Click this link to download it.

Give our team a call at (847) 232-1991 if you have any questions about wiring the Dakota Digital PAC-2800BT with our Infinitybox system.  You can also contact our team directly by clicking this link.

Picture of a Spal Cooling used in our 1967 Mustang wired with Infinitybox

Cooling Fan In-Rush Current

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We get a lot of questions about cooling fans and whether or not you can drive them directly from a POWERCELL output without a relay.  In this post we’re going to talk about cooling fan in-rush current and show you what this looks like.

Any motor has an in-rush of current that flows through it upon start up.  To keep this simple, the windings of the motor look like a short circuit until they start to turn.  At start up, the current flow through the windings is high but settles down to a steady-state current level when the motor gets to its operating speed.  This peak in-rush current can be 4 to 8 times the steady-state current, depending on the motor.

When you buy a typical cooling fan, the manufacturer will tell you that you need a high-current relay to switch the fan on and off.  Typically these relays are 40 or 70-amps.  You need to use a relay with contacts that are sized to handle the in-rush current that flows to the motor.  With our Infinitybox system, we don’t use relays.  We use MOSFETs designed to control inductive loads like motors.  The point of this blog post is to show you what the in-rush looks like on a typical cooling fan.

We used the cooling fan in our 1979 Jeep CJ7 to get a real-life example of what this in-rush looks like.  The fan has a 16″ diameter and we powered it directly from the Jeep’s battery.

Here’s how we collected the data for this graph.  We used a precision current shunt in series between the battery and the cooling fan.  We used a Keysight DSOX1202G Digital Storage Oscilloscope to measure the voltage drop across the current shunt.  The shunt that we used was calibrated to 100 mV per 1 amp of current.  The battery was fully charged to 12.7 volts and the fan was mounted in the radiator shroud against the radiator.  We used a switch to trigger the fan and captured the waveforms.  This picture shows the current flowing to the cooling fan motor over time.

Example of the start-up current flowing into a engine cooling fan

Example of the start-up current flowing into a engine cooling fan

You can see that there is an in-rush of current flowing to the cooling fan motor when it starts.  This in-rush peaks at about 43 amps then settles down to a steady-state current flow of 12.3 amps.

Our POWERCELL outputs are designed to carry a steady-state current of 25-amps.  The MOSFETs that we use have surge current rating of over 100-amps and the terminals that we use have surge current ratings of 70-amps.  Running a cooling fan like the one in our Jeep is very easy for our POWERCELL to switch directly from an output without a relay.

Our Infinitybox system has an added feature that you can’t get from a relay.  Since we are using MOSFETs, we can do something called Pulse Width Modulation or PWM.  This lets us turn the POWERCELL outputs on and off thousands of times each second.  Using PWM lets us efficiently control the flow of current from a POWERCELL output.  For fans, we do something called soft-starting.  This lets us gradually ramp up the current to the fan to smooth out the in-rush current.  We’ve blogged about this before.  You can read it here.  

Stay tuned for a follow up post that will show the effect of PWM on the in-rush current flowing to our Jeep cooling fan.  Click here to contact our team if you have any questions about this post or anything else related to wiring with the Infinitybox system.

Example of a typical radiator temperature switch

Cooling Fan Switch

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The next step in our 1967 Mustang wiring process is to wire the cooling fan switch.  There are a few different ways to do this depending on how you have your car set up.  In a previous post, we talked about wiring the cooling fans to the POWERCELL output.  This link will take you to that post.  In this post, we are going to talk about wiring the MASTERCELL input wire to trigger the fans.

Remember how our system works.  The switches connect to the MASTERCELL.  The loads connect to the POWERCELL.  There is never a direct connection between the switch and the thing that you are switching.  All of that is controlled inside the Infinitybox system.

The most common way to wire the cooling fan switch is to use a temperature switch.  This is usually threaded into the radiator.  When the coolant temperature exceeds a set point, the switch triggers the cooling fans.

Inside the temperature switch, there is a bi-metal switch that is set for a specific temperature.  Typical temperature set points are 180 F, 185 F and 190 F.  When the coolant temperature hits this point, the bi-metal element in the switch flips.  There are two main different types of temperature switches.  The most common has a single terminal on it.  This picture shows a common 1-terminal temperature switch.

Example of a typical radiator temperature switch

Example of a typical radiator temperature switch

If you have this type of switch, you are going to connect your MASTERCELL input wire to the quick-disconnect terminal on the switch.  The switch grounds to the chassis through its metal body.  When the temperature exceeds its set point, the switch closes internally which connects the quick-disconnect terminal to ground.  This triggers the MASTERCELL input, which sends a command to the front POWERCELL to turn on the cooling fan output.  When the coolant temperature drops below the set point, the switch opens internally.  This disconnects the MASTERCELL input from ground.  The MASTERCELL sees this change and sends a command to the front POWERCELL to turn off the cooling fan output.

Other temperature switches have two terminals.  This picture shows a good example.

Example of a two-terminal temperature switch

Example of a two-terminal temperature switch

In this case, both of the terminals are isolated from the metal body of the switch.  You connect your MASTERCELL input to one of the terminals and connect the other terminal to ground.  There is no polarity to this switch so you can use either terminal for the MASTERCELL input connection.  Outside of that, this switch works the same way as the single terminal switch.  When the coolant temperature exceeds its set point, the switch closes internally which electrically connects the two terminals together.  This connects the MASTERCELL input to ground.

This picture shows you generically how to wire a temperature switch to your MASTERCELL input.

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Here is an important note about temperature switches and temperature senders.  There is a big difference between them.  The temperature switch turns on and off at a set temperature.  The temperature sender is what controls your temperature gauge.  You cannot connect your cooling fan input from the MASTERCELL to your temperature sender.

You can also use your ECU to trigger your cooling fan input if it has that capability.  The important thing to understand is whether the ECU trigger is a ground trigger or a positive trigger.  The manual for the ECU will get you more information.  You need to wire these differently if they are ground or positive triggers.  This picture will show you how to wire these two different types of triggers.

Image of wiring diagram showing how to wire the cooling fan trigger from an ECU to the Infinitybox MASTERCELL

Image of wiring diagram showing how to wire the cooling fan trigger from an ECU to the Infinitybox MASTERCELL

If the ECU has a ground trigger for the cooling fan, we recommend installing a diode to buffer the MASTERCELL from the ECU.  If it is a positive trigger, you must use a relay or an inVERT Mini to flip the signal to a ground trigger.  See the picture above for more details.

Our customer is using the Ford Coyote crate engine in this 1967 Mustang.  The Ford ECU has a temperature sender that measures the coolant temperature.  Based on this temperature, the ECU has an output that is designed to trigger a cooling fan.  We have a dedicated wiring diagram on our website that shows you exactly how to wire the cooling fan trigger to the Coyote ECU.  You can download the wiring diagram for the Coyote ECU by clicking this link.  The Coyote ECU has a positive cooling fan trigger.  You must use an inVERT Mini to flip this signal.  The wiring diagram shows you how to do that.

The resources section of our website has wiring diagrams for many different ECUs.  These will show you how to wire the cooling fan trigger from the ECU to your MASTERCELL.

Click on this link to contact our team with any questions about wiring your cooling fan switch.

 

 

Picture of wiring diagram showing how to wire the FAST EZ-EFI fuel injection system with the Infinitybox system.Copyright Infinitybox, LLC 2021. All Rights Reserved.

Wiring the FAST EZ-EFI

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Our Infinitybox wiring harness can be used to provide switch electrical power to just about anything in your car.  This post shows you what you need for wiring the FAST EZ-EFI system.

First, installing any fuel injection system is a process.  Familiarize yourself with the instructions for the EZ-EFI system.  You can download them at this link.

Wiring the EZ-EFI is pretty straight forward.  You are going to use the ignition output on your POWERCELL to supply the switched 12-volts for the EFI system.  The MASTERCELL and POWERCELL in your 20-circuit harness replace the need for the relays to control the fuel pump and the cooling fan.  Connect the wires in their harness per this diagram.

Picture of wiring diagram showing how to wire the FAST EZ-EFI fuel injection system with the Infinitybox system.

Picture of wiring diagram showing how to wire the FAST EZ-EFI fuel injection system with the Infinitybox system.

It is important that you install the diodes that are shown in the diagram.  Our recommendation is to use a 1N4001 diode.  You can purchase these easily on-line.  Please note that the orientation of the diode is important.

You can download a PDF of this wiring diagram by clicking this link.

Give our technical support team a call at (847) 232-1991 if you have questions about wiring the FAST EZ-EFI system.

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELLCopyright Infinitybox, LLC 2021. All Rights Reserved.

Wiring a Cooling Fan

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We recently blogged about how you connect the Infinitybox MASTERCELL to the Holley Dominator ECU.  The next thing that most guys ask about is how to wire a cooling fan.  With the Infinitybox 10 and 20-circuit Harnesses, this is very easy.

Remember that the POWERCELL acts like the fuse and relay box.  Built in the cell is the switching device, called a MOSFET, that turns the output on and off.  It also includes a fuse to protect the wiring harness against short circuits or other over-current events.  You can use the Infinitybox system to control your cooling fan and in most cases, you can eliminate the need for a relay and separate fuses.

The cooling fan must turn on when the engine temperature reaches a set point.  When the engine temperature cools down, the fan should turn off.   There are two main ways to do this.  Traditionally, you have a thermostatic switch in the radiator or modern ECUs have their own temperature sensors to trigger the fan.

In the first case, you are installing a thermostatic switch into the radiator or the engine block.  Most of these switches have a single terminal on them.  They have a mechanism built inside that electrically connects that single terminal to its case when it reaches a set temperature.  This case is connected to ground by being screwed into the radiator or the engine block.  When the temperature drops, the electrical connection between the single terminal and ground is broken.

The MASTERCELL inputs work by being connected to ground.  To wire the MASTERCELL input to the thermostatic switch, simply connect the input wire for the cooling fan to the terminal on the switch.  See the configuration sheet that came with your kit for the right wire color and connector.

Once you have the input connected to the MASTERCELL, connect the cooling fan output on the POWERCELL to one wire on the cooling fan motor.  The other wire needs to connect to the chassis for ground.  We recommend using a 25-amp fuse in the POWERCELL output to protect this wire.

This picture shows in detail how you connect the MASTERCELL input to the temperature switch and how to connect the POWERCELL output to the cooling fan motor.  You can also download a PDF of the wiring diagram here.

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Image of wiring diagram showing how to wire a thermostatic cooling fan switch to the Infinitybox MASTERCELL

Most ECU’s have a trigger that is used to control the cooling fan.  They have a sensor that measures engine temperature and they use an external trigger to turn the fan on and off.  These cooling fan triggers can either ground switch the cooling fan or they can positive switch the trigger.  The manual for the ECU will describe whether the trigger is ground switched or positive switched.

As described above, the MASTERCELL inputs work by being pulled to ground.  When the ECU ground switches the cooling fan trigger, it internally grounds the wire when it wants the fan on.  In some cases, the voltage on this trigger may float or get pulled to battery voltage when the cooling fan is supposed to be off.  This voltage needs to be blocked from flowing back  into the MASTERCELL input.  To do this, solder a diode in series between the MASTERCELL input and the trigger wire on the ECU.  The recommended diode is a 1N4001 and can be easily purchased on-line.  When installing the diode, the stripe on the diode should face towards the trigger wire on the ECU.  This will not work correctly if the diode is wired in backwards.

If the cooling fan trigger on the ECU positive switches the cooling fan signal, you need to invert this to a ground trigger for the MASTERCELL.  You can do this with a relay.  This link will take you to a diagram showing how to do this.

The easier way to convert the positive switch signal from the ECU to a ground switched signal is to use one of our inVERT Mini modules.  These are small and fit easily into the harness.  This link will take you to more information on the inVERT Mini.

Once you have the MASTERCELL input wired to the trigger on the ECU, you need to wire the POWERCELL output to the fan.  This is done exactly the same way as described above for the thermostatic switch example.  Connect the cooling fan output on the POWERCELL to one wire on the cooling fan motor.  The other wire needs to connect to the chassis for ground.  We recommend using a 25-amp fuse in the POWERCELL output to protect this wire.

This picture shows in detail how you connect the MASTERCELL input to the ECU and how to connect the POWERCELL output to the cooling fan motor.  You can also download a PDF of this wiring diagram at this link.

Image of wiring diagram showing how to wire the cooling fan trigger from an ECU to the Infinitybox MASTERCELL

Image of wiring diagram showing how to wire the cooling fan trigger from an ECU to the Infinitybox MASTERCELL

Sometimes, a customer may want to have a bypass switch that they can use to turn on their cooling fans.  This is usually a toggle switch on the dash that will turn on the fan at any time, even when the engine is not up to temperature.

In the case where you have a temperature switch, you simply wire the bypass switch in parallel.  This means you splice into the MASTERCELL input wire that is going to the temperature switch.  You connect the splice to one side of the bypass switch and you ground the other side of the switch.  You can see this shown in the wiring diagram for the traditional temperature switch case.

If you’re controlling the fan through the ECU, you do the same thing.  You splice into the MASTERCELL input wire for the cooling fan that is going to the ECU.  You connect the splice to one side of the bypass switch and you ground the other side of the switch.

Please let us know if you have any questions about how you wire your cooling fans with our Infinitybox 10 and 20-circuit harness kits.  You can reach out technical support team at (847) 232-1991 or email us at sales@infinitbox.com.  You can also contact our team by clicking this link.