So, after finding out that all three of my ECUs are interchangeable, I put the one which I believed had the damaged transistor into the 92, and checked the function of things. Absolutely everything works... including the CEl...

The good news is that my ECU is fine, but the bad news is I still have something going on which is preventing the CEL from functioning in the car I’m working on. 

After making this discovery I reinstalled the ECU in the car with the issue and got to work tracing things for what feels like the thousandth time.

I absolutely, 100% have the two wires hooked up to the proper locations (one to 12v power and one to pin 2 of the ECU. I’ve swapped multiple bulbs which I know work with no change. The voltage gets all the way from the IG key position, through the bulb, and all the way to pin 2. 

Is the ECU not what grounds the CEL to check function before the engine is started? This is the only thing that really makes sense to me, but maybe someone else can help out.

The CEL bulb should be the same number bulb as in your 92. If it draws too much current the ECU transistor may not be able to make it light. Some times they use an Emitter resistor to ground to protect the transistor from a shorted bulb.

If the bulb is correct, what it sounds like, is there is an input to the ECU missing or incorrect causing the ECU to not switch the CEL on with the key. In other words the ECU does not know you turned the key on, or it thinks the engine is running and does not switch the CEL light on.

14 minutes ago, Rampage said:

The CEL bulb should be the same number bulb as in your 92. If it draws too much current the ECU transistor may not be able to make it light. Some times they use an Emitter resistor to ground to protect the transistor from a shorted bulb.

If the bulb is correct, what it sounds like, is there is an input to the ECU missing or incorrect causing the ECU to not switch the CEL on with the key. In other words the ECU does not know you turned the key on, or it thinks the engine is running and does not switch the CEL light on.

Exactly what I was thinking, but I’ve checked all power into the ECU from the ignition switch and it has power in where it should when it should according to the FSM diagrams. If it didn’t know it was running, the car wouldn’t actually run because it needs the ECU to control its functions right?

I’m not sure how to go about tracking down what input could be missing aside form checking FSM diagrams, using a multimeter, and tracing wires. Which I feel I’ve done to the best of my ability. 

Any suggestions?

Well, you have done a super good job so far, because it runs.

I hope you find the missing link.

I've got a lot of work to do tomorrow, swap two front axels, charge the A/C in the van, put a window air conditioner in the house and finish up a laptop. Got to go.

7 hours ago, Rampage said:

Well, you have done a super good job so far, because it runs.

I hope you find the missing link.

I've got a lot of work to do tomorrow, swap two front axels, charge the A/C in the van, put a window air conditioner in the house and finish up a laptop. Got to go.

Much appreciated, good luck on your projects as well!