Author Topic: Under the dash harness  (Read 2392 times)

Offline Smitty31

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  • 1979 GMC High Siera 4wd & 1986 custom deluxe 2wd
Under the dash harness
« on: February 19, 2018, 05:14:35 AM »
1986 c/10 4.3 v6 automatic w/o air I am changing my truck to a a/c cab. I have all the parts off of a 1987 c/10. But I need a a/c wiring harness. My question is this I have long wanted to get rid of the dummy lights. If I change the harness and get one that is for mechanical gauges what else will I need to change. I assume the sending units.
IF ITS WORTH DOING. THEN ITS WORTH DOING RIGHT.

Offline Smitty31

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Re: Under the dash harness
« Reply #1 on: February 19, 2018, 04:50:58 PM »
Have I posted this in the wrong section?
IF ITS WORTH DOING. THEN ITS WORTH DOING RIGHT.

Offline Jason S

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Re: Under the dash harness
« Reply #2 on: February 19, 2018, 07:16:10 PM »
Quote
If I change the harness and get one that is for mechanical gauges what else will I need to change.

Check out this thread. The linked thread references a 1979, but I believe it's the same for 1986:
 http://forum.73-87chevytrucks.com/smforum/index.php?topic=34794.msg295436#msg295436

Here's another thread:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,22075.0.html

« Last Edit: February 19, 2018, 07:18:00 PM by Jason S »
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"

Offline Smitty31

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Re: Under the dash harness
« Reply #3 on: February 20, 2018, 10:38:14 AM »
Thanks for the info that will be handy down the road. But I have to buy a new harness for a/c since my truck is not a a/c truck. So I was going to buy a harness for mechanical gauges as well. Figure I will have to change out sending units but wasn't sure what else? Has anyone else done this job
IF ITS WORTH DOING. THEN ITS WORTH DOING RIGHT.

Offline 75gmck25

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  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Under the dash harness
« Reply #4 on: February 21, 2018, 10:59:58 AM »
GM changed things over the years, but for my '75 they used the same harness for both gauges and lights.  The difference is in the sending unit and the dash cluster, not the wiring.   If you happen to find a tach cluster, that does have a separate wiring plug for the tach.

I am a little confused about your cab swap.  Did you swap the full '87 cab with A/C, or did you just pull A/C parts and try to move them to the '86 cab.  Do you have the controls and the other pieces under the hood (large A/C plenum, relays, etc.)?  If you don't have a complete donor vehicle it might be easier to just buy a Vintage Air system and install it.

I have been working on my A/C on and off over the years to keep it running, so I have a similar interest in understanding all the wiring.  If you pulled the A/C controls off the donor truck there should be a wiring pigtail on the back.  From there you can just match up wiring colors and run the lines through into the engine compartment.  I think there are only 5 wires that go through the firewall for all the HVAC controls.

I could scan in some of the diagrams for my '75 wiring, but it would be better to use one that matches your truck.  They changed some of the electric features over the years (3 speed vs 4 speed blower, blower always on vs. having a true off position), and they also changed how the max A/C setting works (in my truck you just move the temp slider far left past a detent, and that is max A/C; in later trucks there is a position on the controls that says Max A/C).

Bruce

Offline Smitty31

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Re: Under the dash harness
« Reply #5 on: February 26, 2018, 06:00:40 PM »
I found a 87 truck got everything and I mean everything  duct work vents relays controls condensor compressor brackets bolts and the dog house on the outside i think thats what your calling the Pentium. Except the harness. But have a harness I'm going to buy this week. The only head ache I have now is cuting a hole in the fire wall but I made a template out of card board. Does the fire wall also need a drain tube for condesation? I PAID the guy 120.00 and he is selling the harness for 20.00 Also this week I'm buying a complete instrument cluster mechanical 20.00, a spare tire carrier 10.00, door mirror set 20.00 ,and the plastic shields that go in the bottom of the fenders for 10.00. This guy parts out old square body's he is my new best friend lol. Later a steering collum with tilt and a over drive transmission for 250.00
IF ITS WORTH DOING. THEN ITS WORTH DOING RIGHT.