Wiring up in smoke....

#1

I just dropped a used engine in my spec e30, went to fire it up and almost did literally…one of the wires from the main relay went up in smoke. After I got back from the liquor store, I investigated a little more, it is a red wire with yellow tracer, it is paired with the Red/blue coming out of the main relay. I could not find it in the other 4 harnesses I have or in the Bentley book, the engine is out of an 88 iC and I called a tech and he could not find it in the factory lit, although he did not have the iC specific diagram…

What is it and why did it fry? After the wire burned in two the car started and ran…how could it have not damaged the relay?

Al

#2

I had a quick look at an 88 ETM and see 0.75 size RD/YL wires between the over voltage protection relay and the ABS electronic control unit and the ABS hydraulic unit. I don’t see a red/blue wire on the diagram I have, though. If there was something wrong with the ABS ECU, it could cause a short for the RD/YL wire.
bruce

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#3

2nd page

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#4

Don’t know if it’s the same, but when I put a 90 motor into an 89 car, it also shorted a wire going into one of the relays on the strut tower.

A tech told me the airbag and non-airbag wiring was different, and we chose to replace the harness with the one that matched the car. Don’t know if it would have started as yours did after the smoke cleared, because there were other reasons why the car didn’t start that first time…

#5

The red/yellow goes to pin 20 of C101 on the late model harness I have. The only listing of the pinout of C101 that I’ve found shows pin 20 as being N/C. Interestingly, the body side of C101 on my 87 has a socket for pin 20, but the original engine harness doesn’t have a pin in the 20th position??? A further check shows 1 ohm of resistance from pin 20 (body side) to ground.

That would explain the smoke and probably explains why everything works even with the wire fried.