Wiring Harness - Swap Needed? (Page 1/1)
Vicophine JUL 24, 03:10 PM
I officially started my engine+trans swap yesterday, going from the 2.5L to the 2.8L V6.
Upon starting this, I realized that my donor car's wiring harness is just about shot, lots of melted wires, frayed connections, etc.

My donor car is a 85 GT, 4-speed manual.
My recipient is an 88 4 cylinder 3-speed manual.

Can I use the existing wiring harness/wires or should I start looking for a "new" complete wiring harness?
ericjon262 JUL 24, 04:40 PM

quote
Originally posted by Vicophine:

I officially started my engine+trans swap yesterday, going from the 2.5L to the 2.8L V6.
Upon starting this, I realized that my donor car's wiring harness is just about shot, lots of melted wires, frayed connections, etc.

My donor car is a 85 GT, 4-speed manual.
My recipient is an 88 4 cylinder 3-speed manual.

Can I use the existing wiring harness/wires or should I start looking for a "new" complete wiring harness?



I take it the 88 was a 5 speed not 3 speed.

there's a couple of differences between the 85 and 88, mainly, the 85 has the reverse light switch mounted to the shifter, whereas the 88 has it on the trans. you're really best off getting a 87-88 V6 5 speed harness in good shape, then carefully inspecting it and cleaning it.

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pmbrunelle JUL 24, 07:01 PM
I think OP wants to use a 2.5 harness on a 2.8 engine. It's quite different, I wouldn't bother.

I'd suggest looking for any used Fiero 2.8 harness you can find. They're all mostly the same, regardless of transmission or model year. Any 2.8 harness can easily be tweaked to fit your car / engine / transmission combination. By tweaking, I mean depin connectors, change pin positions as necessary, untape, run a new wire, retape and reloom, that sort of thing.

Technically, supposing that you want to use the 4-speed manual that came with your 2.8, no drop-in wire harness exists from the factory, as no 1988 Fieros came with the 4-speed manual from the factory.

Therefore, you would be stuck with harness tweaks no matter which harness you started with.
Vicophine JUL 24, 07:12 PM

quote
Originally posted by ericjon262:


I take it the 88 was a 5 speed not 3 speed.

there's a couple of differences between the 85 and 88, mainly, the 85 has the reverse light switch mounted to the shifter, whereas the 88 has it on the trans. you're really best off getting a 87-88 V6 5 speed harness in good shape, then carefully inspecting it and cleaning it.



My bad, I meant the 88 has a 3 speed AUTOMATIC. Going to be replacing that with the 4-speed MANUAL.

I'll keep looking, other than maybe eBay, are there any reputable sites that I could purchase a wiring harness?
Vicophine JUL 24, 07:16 PM

quote
Originally posted by pmbrunelle:

I think OP wants to use a 2.5 harness on a 2.8 engine. It's quite different, I wouldn't bother.

I'd suggest looking for any used Fiero 2.8 harness you can find. They're all mostly the same, regardless of transmission or model year. Any 2.8 harness can easily be tweaked to fit your car / engine / transmission combination. By tweaking, I mean depin connectors, change pin positions as necessary, untape, run a new wire, retape and reloom, that sort of thing.

Technically, supposing that you want to use the 4-speed manual that came with your 2.8, no drop-in wire harness exists from the factory, as no 1988 Fieros came with the 4-speed manual from the factory.

Therefore, you would be stuck with harness tweaks no matter which harness you started with.



Ahh, for some reason that never occurred to me that a 4-speed was never offered... This makes a lot of sense. Could my existing 88 harness be tweaked at that point to support the 4-speed V6?
Dennis LaGrua JUL 27, 08:41 PM

quote
Originally posted by Vicophine:


Ahh, for some reason that never occurred to me that a 4-speed was never offered... This makes a lot of sense. Could my existing 88 harness be tweaked at that point to support the 4-speed V6?



A 85 2.8L harness and the respective ECM should be a direct fit. You can use the ECM that came with an auto or stick for a manual application. If its the auto setup you just won't have the shift lamp (if that's important to you) Any other Fiero 2.8L harness/ECM would work as the differences are minor. To use an 88 4 cyl harness to control a V6 engine would be a massive rewiring job. Most of the Duke connectors, including the ECM connector would have to be replaced, new fuel injection, and ignition control wiring added. It would be like starting from scratch. With all the used stuff out there you should be able to find a suitable V6 harness.

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[This message has been edited by Dennis LaGrua (edited 07-28-2019).]