Wiring or AC? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

don t. - 72gmc · 10-20-2023, 07:29 AM

Aint talked to the wife yet(smile) about the next thing I'd like to do w/my truck.
70 GMC Sierra Grande survivor.

At 53 years, some of the under hood wiring should be R&Red. I've fixed some of it as the need arose. Also wondering about inside the cab wires, rear light wires. I don't have any problems, hate the thought of fixing something that aint broke, but have been down the road of small electrical fires in the way distant past.

Truck has factory air. R12. It has a leak. I have a friend who says he has R12, willing to give me some once I fix the leak. Don't really need AC but it would be nice.

Thoughts appreciated....Don.

PS....Im not a big electrical guy, have never worked on an AC system.

**A1971Blazer** · 10-20-2023, 07:42 AM

you can buy the underhood wiring portion of the harness new that will plug right into the bulkhead connector. It's available as original or you can specify HEI, if you have it, and get one already wired for it.
M&H and American Auto Wire both have them.
I purchased a front light harness from eBay that was good quality as well.

MARKDTN · 10-20-2023, 09:37 AM

Underhood wiring is pretty easy to swap over. And as stated if you have HEI you can get a harness made that way which is nice. I have used M&H and 'Lectric Limited factory type harnesses on various things over the years. You don't say how bad the wiring is. If it is burn the truck down bad then that would be a priority.

A/C requires dry and clean inside the lines. If the compressor is not locked up then I would at least try to find the leak so you know what you are up against. Could be a line or hose or just a fitting, could be evaporator or condenser, could be compressor. Each of these is a different level of complexity and expense. But once you have dirt and air in the system it is harder and harder to get it clean again. I would try to find out what is actually causing the leak and re-evaluate.

**pjmoreland** · 10-20-2023, 10:43 AM

You can find a leak in the A/C system by putting some dye in it followed by charging the system. Then you run it for a while and then use a UV flashlight to check for dye. Kind of a bummer to have to do it this way when R12 is scarce, but I don't think there is any other way to find a leak without charging it.

MARKDTN · 10-20-2023, 02:57 PM

With an R12 system if it is already contaminated with air you can probably pressurize it with shop air and use a leak sniffer to find the leak. Once you do this you will have to replace the filter/dryer-but if you open the system to fix the leak you would want to do that anyway. If the system is empty it will already be saturated anyway. R12 (and R22) can be detected in very diluted quantities with a good sniffer. You really need a friend in the HVAC business to help with this part and not spend a fortune.

PbFut · 10-20-2023, 04:21 PM

If not having AC is acceptable for a while, I would probably redo the electrical if you feel it is at end of life. The factory designed fuse protection of the harness was acceptable for the time but it is marginal by today's standards if you are using all the optioned accessories of the truck. My 72 is fairly original and fully optioned, and I added more stuff. I needed to change things a bit for the electric fans and camper battery I added. It was a mistake in hindsight to use electric fans but that is off topic. I needed to modify the shunt wire from the main splice in the harness to the battery. I had to disassemble much of the front harness to do so. I will say that my harness was in remarkably good shape for its age, including the volt reg, horn and headlights. All I really needed to do to the unmodified sections was clean with simple green and contact cleaner. on the connectors. The result was better than expected making the front end look very original and clean The factory did not use adhesive electrical tape. It is simply a vinyl tape wrap. It is easy to find and use once you learn the end technique. You can use electrical tape but it will likely get gummy over time. If you decide to repair, solder all your joints. Use shrink wrap to protect the other wires in the harness, and then vinyl wrap the set for a factory look. If you have time it is very easy to do and way cheaper than buying a harness if you have the time. Harnesses arn't that pricey so if time is an issue, get a new one. Good luck. I had a decent feeling of accomplishment once I got it all figured out. Not having to modify anything will be a snap for you.

10-20-2023, 07:29 AM	#1
don t. - 72gmc Registered User Join Date: Dec 2001 Location: harvard, il. USA Posts: 389	Wiring or AC? Aint talked to the wife yet(smile) about the next thing I'd like to do w/my truck. 70 GMC Sierra Grande survivor. At 53 years, some of the under hood wiring should be R&Red. I've fixed some of it as the need arose. Also wondering about inside the cab wires, rear light wires. I don't have any problems, hate the thought of fixing something that aint broke, but have been down the road of small electrical fires in the way distant past. Truck has factory air. R12. It has a leak. I have a friend who says he has R12, willing to give me some once I fix the leak. Don't really need AC but it would be nice. Thoughts appreciated....Don. PS....Im not a big electrical guy, have never worked on an AC system.

10-20-2023, 07:42 AM	#2
A1971Blazer Senior Member Join Date: Nov 2013 Location: East Tennessee Posts: 2,124	Re: Wiring or AC? you can buy the underhood wiring portion of the harness new that will plug right into the bulkhead connector. It's available as original or you can specify HEI, if you have it, and get one already wired for it. M&H and American Auto Wire both have them. I purchased a front light harness from eBay that was good quality as well. __________________ 1967 C10 Step side 1968 C10 Step side 1970 Chevrolet K/5 Blazer 1972 Chevrolet K/5 Blazer .............

10-20-2023, 09:37 AM	#3
MARKDTN Registered User Join Date: Jan 2011 Location: Chattanooga, TN Posts: 2,142	Re: Wiring or AC? Underhood wiring is pretty easy to swap over. And as stated if you have HEI you can get a harness made that way which is nice. I have used M&H and 'Lectric Limited factory type harnesses on various things over the years. You don't say how bad the wiring is. If it is burn the truck down bad then that would be a priority. A/C requires dry and clean inside the lines. If the compressor is not locked up then I would at least try to find the leak so you know what you are up against. Could be a line or hose or just a fitting, could be evaporator or condenser, could be compressor. Each of these is a different level of complexity and expense. But once you have dirt and air in the system it is harder and harder to get it clean again. I would try to find out what is actually causing the leak and re-evaluate. __________________ '83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project

10-20-2023, 10:43 AM	#4
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,389	Re: Wiring or AC? You can find a leak in the A/C system by putting some dye in it followed by charging the system. Then you run it for a while and then use a UV flashlight to check for dye. Kind of a bummer to have to do it this way when R12 is scarce, but I don't think there is any other way to find a leak without charging it.

10-20-2023, 02:57 PM	#5
MARKDTN Registered User Join Date: Jan 2011 Location: Chattanooga, TN Posts: 2,142	Re: Wiring or AC? With an R12 system if it is already contaminated with air you can probably pressurize it with shop air and use a leak sniffer to find the leak. Once you do this you will have to replace the filter/dryer-but if you open the system to fix the leak you would want to do that anyway. If the system is empty it will already be saturated anyway. R12 (and R22) can be detected in very diluted quantities with a good sniffer. You really need a friend in the HVAC business to help with this part and not spend a fortune. __________________ '83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project

10-20-2023, 04:21 PM	#6
PbFut Registered User Join Date: Feb 2022 Location: Ca Posts: 435	Re: Wiring or AC? If not having AC is acceptable for a while, I would probably redo the electrical if you feel it is at end of life. The factory designed fuse protection of the harness was acceptable for the time but it is marginal by today's standards if you are using all the optioned accessories of the truck. My 72 is fairly original and fully optioned, and I added more stuff. I needed to change things a bit for the electric fans and camper battery I added. It was a mistake in hindsight to use electric fans but that is off topic. I needed to modify the shunt wire from the main splice in the harness to the battery. I had to disassemble much of the front harness to do so. I will say that my harness was in remarkably good shape for its age, including the volt reg, horn and headlights. All I really needed to do to the unmodified sections was clean with simple green and contact cleaner. on the connectors. The result was better than expected making the front end look very original and clean The factory did not use adhesive electrical tape. It is simply a vinyl tape wrap. It is easy to find and use once you learn the end technique. You can use electrical tape but it will likely get gummy over time. If you decide to repair, solder all your joints. Use shrink wrap to protect the other wires in the harness, and then vinyl wrap the set for a factory look. If you have time it is very easy to do and way cheaper than buying a harness if you have the time. Harnesses arn't that pricey so if time is an issue, get a new one. Good luck. I had a decent feeling of accomplishment once I got it all figured out. Not having to modify anything will be a snap for you.



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