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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.

Copyright 2022 Infinitybox, LLC. All Rights Reserved.

Soldering Components In-Line

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Okay… we do our best to not take things for granted.  In all of our blog posts, we always try to give you as much fundamental information on the material that we are presenting.  Every once in a while, we get called out by our customers for not explaining something thoroughly.  This post is intended to fix this.  In a lot of our blog posts and wiring diagrams, we show components installed in-line with a MASTERCELL input or a connection to ground.

In our last blog post, we showed wiring a 10K pull up resistor on a brake-pedal switch.  You can see that blog post here.  In other blog posts, we’ve shown wiring diodes in-line between a trigger on an ECU and a MASTERCELL input.  You can click here to see a recent example blog post.  Someone just asked us an obvious question on our last blog post.  “How do I install the diode or the resistor in the wire”.  We’ll show you how.  This isn’t the only way to do this but it is our recommended way to do this.

There are three important factors to consider when installing an in-line component in a wire.  First, you need to have good electrical connection.  Second, you need to protect it mechanically.  Lastly, you need to protect the joint from the environment.

These steps will show you how to solder an axial, leaded component in-line with a wire.  A leaded part has metal terminals coming off its ends.  An axial part has the leads running along the axis of the component.  This picture shows you a good example of an axial, leaded diode.

Example of a simple diode

Example of a simple diode

 

Speaking of diodes, remember that they have a direction to them.  Check our wiring diagram for proper orientation of the diodes.  Resistors do not have a direction so you can install them either way in your wiring harness.

The first step is to strip back the insulation on the wire you’re connecting to your component.

Next, you want to twist the strands of the copper wire together.  This will make the next steps easier by keeping the strands together.

Next, twist the strands of the wire with the lead coming from your component.  We recommend leaving some length of the lead at the end as shown in this picture.

The next step is to make a good electrical connection between your wire and the lead on your component.  This needs to be soldered.  A good soldering iron and electrical solder will make this job easy.  You want to make sure that you are heating the joint thoroughly and that the solder is flowing between the copper wire and the lead on your component.  When you’re finished, the joint should be shiny.  If your joint looks grey or dull, you need to apply more heat and solder.  We also recommend keeping the solder on the joint between the copper wire and the lead on the component.  You do not want the solder to wick up the copper wire under the insulation.  This will make the joint inflexible and it could fail over time.

Once you have the joint soldered, clip off the extra length of lead on the component.

Repeat this process for the other side of your component.

Now you have a good electrical connection between your wires and your component.  The next step is to protect the component mechanically and from the environment.  To do this, we recommend a good quality heat shrink tubing.  Heat shrink tubing does what its name suggests.  It shrinks around a joint when you heat it.  Cut a length of heat shrink tubing that is slightly larger in diameter than the component that you soldered in line.  You want the length of this tubing to extend past the exposed area of your joint by about 1/2″ on both sides.

Use a hot air gun to heat the tubing and shrink it over the component and the joints.  We know that a lot of guys like to use lighters or torches to do this but we really recommend a hot air gun for better control and safety.

The heat shrink tubing is going to do two important things.  First, it is going to mechanically strain relieve your joints.  This will keep the joints from failing due to vibration of mechanical stress.  We recommend that you zip tie these components in the harness to minimize any bending or movement as an added precaution.  Secondly, the heat shrink tubing is going to protect the joints from exposure to moisture, dirt and other chemicals in your car.

Soldering in-line components in your harness is a simple thing to do.  If you have any additional questions about this, please click on this link to contact our technical support team.