Need help with engine bay wiring

[Benjie]

I bought this truck about 3 months ago for 150$ it's 1985 gmc k10 with a 4spd and a 355with 500 miles on it and the guy ran water through it and cracked the block so I got a junk yard motor and rebuilt it But the wiring is such a mess the PO owner said about 5 different people did wiring on it so pretty every wire is a different color ends have been cut off and and about 4 roles of electrical tape was used I've got power going to the fuse box and all that works is the wipers and driver side blinker

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[gpmorgan]

If you go to autozone website and sign in, there are ele schematics for your truck on there. You will have to search around a bit to find the one you need.

 

[Honky Kong jr]

If I were you I'd buy a book. Wiring diagrams can be overwhelming at first glance but if you trace 1 wire at a time you will get a feel for it.

 

[Benjie]

Yeah first thing I bought when I brought the truck home was a chilton but none of the wires in the book match the ones coming out of the firewall

 

[Honky Kong jr]

Yeah first thing I bought when I brought the truck home was a chilton but none of the wires in the book match the ones coming out of the firewall

Go by pin designation then time my have dis colored the wire insulation as well.

 

[cooperhw]

My electrical guy (who had moved) told me to "take one wire only and route it, fix it, or replace it". Then go to wire #2. repeat. Tie each wire together in as you run them with a couple wraps every so of the of electrical tape so they stay the same length, then as the "branch off", route them separately. There is not that many wires if you look at it individually, daunting if you look at it as a whol

 

[JON79C10]

I agree with Cooperhw, one wire at a time. My 79 was pretty much the same as yours - ugly, butchered and botched. What I did was remove each wire that was connected to something, like HEI + or Tach and mark them up with tape. Then I unplugged the engine harness from the bulkhead and layed the whole thing out on the ground. Taking aside the stuff you marked up you then have the unknown to identify from the diagram. Clean the wires at the harness plug as tan often looks like dirty pink and stripes are often hidden. Then I took a check list of all the items I wanted to power up on my new engine build. Crossed off what was already in the harness, ran new ones to what was missing, resued stuff that could be redeployed. For example I needed a ignition on hot feed for my fan relay but didnt need an electric choke so this was extended down to the fan area. Finally, I dead ended any that were not needed with an insulated crimp leaving a few inches. This means they can be reused later if you wanted. The I just made a neat job of taping it all up. If you have trouble guessing the right length of a wire to run to an item, simply over length it and terminate it when the harness is laid back in. Try to preserve the awkward connections like Alternator and starter motor. Trashed conections can be replaced with new pig tails like from rockauto for most points. If you stagger connectors when splicing the harness it will tape up nicer than 4 all in a bunch. Its also worth pulling and checking every fuse blade inside just in case some have blown, throwing you off track.
Jon

 

[MrMarty51]

I once pulled the entire harness from an AC loader, stretched it out on a peice of plywood and used finish nails to stake down the terminals. Laid out a new harness over the top of the old harness. where needed I clipped off the terminals with a pig tail and soldered and heat shrinked those onto the new harness, terminals that were more like ordinary were just replaced with new.
Amazingly, everything worked after installing the new harness.
I did use wire tags to mark what each terminal was from before pulling the harness.

 

[MikeB]

Wiring diagrams:

81-87 Cab Interior Page 1
81-87 Cab Interior Page 2
81-87 Chassis and rear Lighting
81-87 Front Lighting
81-87 I6 Engine Compartment
81-87 V8 Engine Compartment
81-87 Instrument Panel Page 1
81-87 Instrument Panel Page 2
81-87 computer control wiring

 

[chengny]

All these trucks have 3 separate plugs at the main firewall connector block. One each for front and rear lighting harnesses and another for engine related components (also htr blower, windshield wiper/washer, instrumentation, battery power to the cab, etc.):

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The three harnesses can be unplugged and separated by releasing the single bolt in the middle of the block:

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Just a suggestion; Maybe the best way to do this rewiring job is, rather than try to duplicate the factory wiring, just go to the junkyard and pull the harnesses that you need. The wires will all be the correct color/length and the terminal connections will be appropriate for the associated components. The donor truck doesn't have to be exactly your model year, any 81-87 will have essentially the same wiring. Just cut out what you don't need.

The cab wiring is a mess. I would definitely go the harness transplant route on that.

 

[gmachinz]

Or if you want to take the easy route and save yourself some time, I know a guy who reproduces the wiring harnesses as factory style replacements....here's an egine harness for example....

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[84c10Tony]

That harness is beautiful, someday, if I still have my 84', I would like a good person to install one for the truck, with some added heat protection and that would be fine till I am done driving.

 

[Silverado81]

I purchased the complete engine harness about a year ago, and highly recommend that route if $$ permits. I had to make one modification to get everything working correctly, but it's been working great since.

 

[spanky55amg]

Also, posted on this board, we have most of the electrical diagrams for our trucks.

Don’t buy a book. First they are free here. Second, the chiton book for our trucks are dead wrong or lacking information.

 

[TravisUT]

@gmachinz - How can I purchase one of those wiring harnesses?

Or if you want to take the easy route and save yourself some time, I know a guy who reproduces the wiring harnesses as factory style replacements....here's an egine harness for example....

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