3500 – Wiring

This page is a work in progress while the engine swap is underway.  I am running the engine with a Megasquirt (MS) stand alone engine controller.  The ignition system is the coil packs with Ignition Control Module (ICM) setup used on about every 60 degree V6 throughout the 1990’s and into the early 2000’s.  The MS can easily control the ignition timing of the ICM.   I have an external 7x crank trigger setup for driving the ICM.  It is possible to use the 3500 OEM crank trigger signal, but it require some special software setup.  It is not the typical 58x sensor that I expected.  I found it to be easiest to just use the ICM crank reference output pins.  It is basically the same signal as the tachometer output from the ICM (3 pulses per revolution).

The main connectors tampered with in an engine swap for the Fiero besides the ones going to the controller are C203 (15 pins, between the driver and passenger seat) and half of C500 (34 pins just to the rear of the battery in the trunk).

Fiero Connector C203 Fiero Harness - C203 - ECM connectors- ALDL Fiero Connector C500 Fiero Overhead Harness Layout

(Pictures from 1988 Pontiac Fiero service manual)

C203 has one connector on the engine harness side, but the top and bottom row of pins are two separate connectors coming from the body of the car.  C500 is similar, but the connector on the body of the car is one connector, and the connectors coming from that split into two parts.  Only one of those parts connects to engine parts.  Some of the pins in the other half of C500 go to cruise control, which isn’t exactly connected to the engine.  If you try to remove pins from C500, remember, there is a slide pin that holds them all in place.  If you connector is like mine, it will be so dirty that you do not notice it.  None of the pins will come out if you do not remove this slide and use the Delphi pin removal tool.

In the end I have a harness for the C500 connector to the engine and another harness that goes to C203.  It looks very clean and would recommend anyone doing this swap go this route.  It also makes building the entire harness easier.  Between doing that and my exhaust routing I was able to make the harness much shorter than the factory setup.  This was due in large part to it coming out of the bulkhead and then running under the throttle body.  This kept it away from hot spots too.

I have two documents that I was maintaining to help me remember what goes where.

The harness took a lot of time to plan, and much less time to build.  It took about 15 – 20 hours to build.  I strongly recommend investing in the right parts for the job:

Here is a great write up that I won’t try to reproduce about how to actually make a harness.

My TPS, IAC, and IAT (MAT) sensor wiring is long enough that I can swap from naturally aspirated to the supercharger setup without cutting anything.  I did make an adapter plug for the TPS sensor though, since that one is the only one that is different when doing that swap.

I feel like I could write about the harness build for quite some time, but that there would not be much value for anyone at all.  If you have any questions about anything you think I could help with, just ask.

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