87 Wiring Harness vs. 86 Harness???

[tex_waco_usmc]

Ok, please forgive my ignorance. I feel like a newbie, but only because the trucks Im normally working on are the generation before this one....

The truck I am building is an 86 GMC, but I pulled the complete harness and drivetrain from an 87 GMC with TBI to install in the 86. How much of the harness from the 86 doesnt need to be swapped out with the 87?

What I am getting at is: am I going to have to gut the cab and completely rerun the entire harness or are the two harnesses mostly the same minus a few changes here and there?

Someone please save me some work! LOL

[Greenlee]

I replaced an 87' truck harness with an 89' Suburban harness. I found that once I got everything out and separated it was not as complicated as I thought it would be. There are really several separate system harnesses that simply plug into the fuse box. You will probably find that you can just pull the engine harness and everything related to the TBI and plug it in.

However, since you are going from non-TBI to TBI I'm not sure if it would be easier or better to use the fuse box from the 87'. Other wise you might need some stand alone fuses for the computer/TBI stuff.
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[Greenlee]

Check out the TBI swap build thread that's currently on the first page. Lots of people have done this without swapping the entire harness.
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[tex_waco_usmc]

I still need help with this guys, if anyone can help me out.

From what I can tell it appears that all the underdash harness is the same and the headlight harness is the same...

The only thing that appears different is the computer and the engine harness.

If anyone knows any different please let me know.

[86c20]

me too. i just want to know if i can take the engine harness out and put it in the 88 harness i have

[tex_waco_usmc]

Well first part I found different was the plug that is the tail lights for an 87 also has wires that control the fuel pumps in it! That was an easy fix! It is looking like I'm gonna have to change the entire under dash harness, though! It sucks but it will get the truck running!
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[esbstuff]

Originally Posted by tex_waco_usmc

Ok, please forgive my ignorance. I feel like a newbie, but only because the trucks Im normally working on are the generation before this one....

The truck I am building is an 86 GMC, but I pulled the complete harness and drivetrain from an 87 GMC with TBI to install in the 86. How much of the harness from the 86 doesnt need to be swapped out with the 87?

What I am getting at is: am I going to have to gut the cab and completely rerun the entire harness or are the two harnesses mostly the same minus a few changes here and there?

Someone please save me some work! LOL

Sorry to tell you but you will have to change everything except the talight harness... Carb vs TBI is all differant. Now if you have power windows and or power locks, you can leave that alone as it won't need changed either.

[tex_waco_usmc]

I haven't tackled the main harness but for the taillight/fuel pump harness I just removed the two extra pins out of the 87 harness and stabbed them in the proper holes in the existing harness. ( I didn't want to rerun wires all the way to the taillights! )
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