Modifry's S2000 ECT Installation

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Wiring Diagram
Full Manuals (includes wiring diagram) AP1 Manual AP2 Manual
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This page is only an overview, download the manuals and review before purchase.

The ECT Display Driver is a small module with a removable wire harness that mounts behind the driver's foot well cover.
All wiring connections are near the ECM and only 4 wires are needed for basic operation:

	+5v power from the ECM (T-tap)
	Ground
	ECT sensor (T-tap at ECM)
	Dash temperature gauge (must cut dash gauge wire)

If you want to use the Alarm Output feature 3 more wires are needed:

	Ground (must be separate from the module's ground)
	Module output to your alarm device (sounder or indicator light, not included)
	+12v power for your alarm device

Here's the wiring diagram for the ECT Module. As you can see, you will have to splice into the ECM (or EMS) wiring for the ECT sensor, +5v power, and ground.

You will also have to cut the wire going to the dash Temperature Gauge and connect the gauge end of the wire to the ECT module.

AEM users see notes at the bottom of this page.

Here's a photo of the driver's foot well after the cover is removed, showing the ECM and the connectors you will be connecting to.

Here's a closeup of the stock ECM showing the two connectors with the ECT sensor wires and the Temp Gauge wires.

You will have to tap into +5v power and the ECT signal wire at the ECM, and connect a separate ground wire. You will also need to cut the Temp Gauge wire and connect to the end that goes to the gauge.

If you install a sounder or light for an over-heat alarm (optional) you will need to install additional wiring.

Special note to AEM EMS owners:

Some customers have had difficulty getting the gauge to display properly on AEM EMS systems. I know of at least two cases where, after some troubleshooting, customers verified the voltage on the ECT sensor wire would change when other electrical loads turned on and off. Sometimes the change was only 50 or 60 millivolts, sometimes several hundred millivolts. In particular the radiator fan and AC system seem to cause the ECT voltage to fluctuate, and that of course makes the gauge display fluctuate too.

These symptoms are classic examples of a "ground loop". Ground loops occur when current for one electrical circuit inadvertently flows through the ground leg of another circuit. Here's an extreme example: pull the fuse for one of your HID headlights (low beam), then turn ON the low beam lights and check out the front of the car. Not what you expected, huh?

You probably figured one light would work and the other would remain off. But in fact you will see one light come on normally, the other HID will flicker, and both high beams will be lit dimly. This is how a ground loop works. Power from the working low beam circuit back-flows through the high beam filaments and makes it's way to the low beam with the missing fuse. Because current passes through both high beams and the HID (one big series circuit) they each get less than 12v, causing the high beams to glow faintly and the HID to flicker. Cool.

With the ECT sensor, it's a similar effect. If the sensor ground wiring is not exactly perfect, ground current for other devices will flow in the sensor ground wire, causing a voltage change that the ECT module (and sometimes the EMS too) will interpret as a different temperature. How does ground current get into the sensor ground? Think about it - how does ground current get anywhere in a car? It flows through the chassis. We think of the chassis as "one big ground lug" but in fact it's "one big resistor". OK, it's a resistor with very low resistance, but when you pass a large current through even a low-ohm resistor you will get a noticeable voltage drop.

So the question is - did you move ANY ground wires in your car? Did you remove or re-route any wiring to the engine block? Did you move a ground lug or terminal from one bolt to another one "close by"? Did you move the ECM and use a new ground for it? Did you ground the ECT module anywhere other than directly at the ECM or at the ECM sensor ground?

Since the ECT sensor operates with very small voltages, even that "close by" ground bolt might not be close enough to maintain the ground integrity of the sensor wiring. If there's only 1/100 of an ohm resistance between the two chassis points (original ground point and your new one), the radiator fan current (30-40 amps) could cause 300-400 millivolts change in the ECT voltage. That 0.3 volts won't affect the radiator fan, but will surely screw up the ECT reading!

The bottom line: If you have ECT gauge problems, the first thing to do is put a meter on the ECT sensor wire and measure the voltage. Look it up in the voltage/temperature table in the manual to see if it's in the range it should be. Turn everything electrical ON and OFF and see if the sensor voltage changes. It shouldn't change by more than a few millivolts no matter what is turned ON or OFF. If it makes any sudden changes with electrical activity, then you've got a ground loop.

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