Toasted wiring harness

[70 Long Fleetside]

Hey group,
I've had my 70 C10 for about 2 1/2 years, and it has run pretty great most of the time, except for an intermittent electrical problem, 2 ignition switches have burned out. The first one burned out right after I got it, I replaced it wondering what would cause that, and drove it for over a year before it melted another one. I of course was worried and should have posted then!
Yesterday I was cruising along and smoke started coming out of my dash, it died, and I opened the hood to smoking wires from the battery to the fuse box, really happy I didn't catch fire.
Anyways I knew I needed to rewire the thing, and now I have to, but does anyone have any idea what would melt the whole harness?
I bought the truck with about 10k on a fresh 400 sb, originally a 6, and have put on about another 10k on it. The guy I bought it from got it to flip and didn't know anything about the work that had been done.
Here's to wrenching, hope I didn't burn up my alternator, starter etc. Time to install the HEI ignition I bought a year ago, haven't looked but the last time I replaced the ignition switch it melted the points and burned out the coil.
It's an original paint no rust barn find that showed 30K on the title and it looked like a 30k body, though there are a few dings. It has 46k miles on it now.
Thanks in advance for any help.

[ujsf01]

If I am understanding you correctly, you mean the main red wire that comes from the little junction block over by the battery. This wire should be protected at the battery end by a fusible link that would melt before melting the rest of the circuit in the case of a short. If someone has previously removed the link, then that would account for the damage to the entire harness. That wire should go to the ignition switch, horn relay, alternator, voltage regulator, headlight switch, as well as the fuse block. The kicker here is that red wire is hot all the time, key on or off. That means if there was a short anywhere in this wire and it had no fusible link protection, it wouldn't matter if the truck was running or not for the meltdown to occur. That said, odds are the problem is somewhere on the output side of the ignition switch, especially given the history of eating igntion switches. If the issue is an intermittent short that occurs while driving, replacing the harness will take care of the problem. However, if there is a component that is causing the problem, it will probably damage the new harness and just add more to the frustration level. If you can lay your hands on a correct wiring diagram, I bet you could find the source of the issue in a relatively short period of time. The pink wire and brown wire on the switch go to the fuse block, the green wire is for the temp gauge/light circuit and the tan wire is for the brake warning system. Hope this info helps. These trucks are pretty simple electrically. Feel free to contact me if I can help you any further.

[70 Long Fleetside]

Thanks Steve.
I went and looked at it, you are correct, the red wire had no link and melted the other wires that were tied to it.
Do you have any advice on parts? Toe to tail kits are $500, and there are 21 circuit kits on ebay for less than $150, and the harness was new 3 years ago. If I chase everything down with the wiring diagram can I get away with replacing just the wires that were tied to it? Let me know what you would do.
Also I think the wiring was the same for all the engine setups, and at least the sb V8's are the same, is that true? The 6 was replaced with a sb 400 which I don't think was offered as an option for a 70 but I don't think that should effect anything, let me know if I am wrong.
I really appreciate your help. I have a bit of experience working on my own cars and a fair understanding of everything but I am by no means a mechanic.
Best,
Avery

[70 Long Fleetside]

Well, I ran a wire to the battery and one to the coil at the junction box and touched off the solenoid and it fired and sounded like everything was ok. I ran it for less than a minute. Don't know if that was dumb but I wanted to know what I was in for on the parts front and I didn't think It would hurt anything that wasn't already fried. The starter and ignition are working which is a relief, but I'm still going to bypass the resistance wire to the coil and put in the HEI with the new harness so I don't have to carry extra points and condenser everywhere I go, maybe I'll get a little more power and gas mileage along with the reliability.
Feel free to offer suggestions.
Thanks,
Avery

[michael bustamante]

theres guys here in the parts for sale section selling engine wiring harnesses if that would weork for you, depending on your gauges, it changes the engine harness. if you have the ammeter then thats the engine harness with the two little inline fuses on either side of the radiator.

[70 Long Fleetside]

Michael,
Sweet, thanks! I have the free membership so I can't see the classifieds. I may just upgrade.
Avery

[70 Long Fleetside]

I'm wrong, I just went back and I can see the parts. Thanks!

[michael bustamante]

sure thing man. also a 67-68 harness wont plug into your firewall so be wary of that

[70 Long Fleetside]

Thank you! My truck is from Albuquerque. That's why there is no rust.

[Orange Crate]

Originally Posted by 70 Long Fleetside

It's an original paint no rust barn find that showed 30K on the title and it looked like a 30k body, though there are a few dings. It has 46k miles on it now.

I had a similar situation happen many years ago and spent weeks going through the entire harness, cutting out bad sections of burnt wire and soldering in new pieces with heat shrink. It worked but after all that I regretted NOT getting a new harness. From the quote above I vote in your trucks favor for a new harness (trust me it's worth it)

[70 Long Fleetside]

I'm thinking its probably a good idea.
Thanks!
Avery

[ujsf01]

I sell and install American Autowire harnesses and would highly recommend their Classic Update kit. I have one in my 67 C/10, and have installed many others in various vehicles for customers. They cost a little more, but the completeness of the kit is worth it!

[oldertruckfan]

don't chop the harness up. you'll regret it later on. As a person who REALLY hates electrical, I would opt for the entire front harness. I'm in the process of tearing my truck down for a rebuild and the harness replacement is on the list! better to be safe with tons of money in the truck than watch it burn to the ground on the side of the road.

[70 Long Fleetside]

Thanks guys, you've been really helpful.

[CST10]

Entire harness is the way to go. The fusible link could have saved you a lot if it was there. Mine saved me recently b

[70 Long Fleetside]

For sure. It doesn't look like it's going to be too bad, its a base truck, I pulled a lot of the old harness today. Plus with the new harness I'll be wired for A/C, which is the next project. I should do disc brakes first, but living in Austin it's no fun to drive on those 107 degree days. Hopefully I can get the original AM radio to work now, nothing like listening to Willie Nelson in mono! I'm going to hide a bluetooth stereo while I'm at it. I think it will be fun. It's going to delay my 73 Triumph Bonneville build, but hopefully not by too much.
Steve, thanks, I found an American Autowire priced reasonably on ebay, should have it for next weekend.
I'll tell you what I screwed up soon!

[Raider Rudy]

The exact same thing happened to me 2 months ago! I bought a 68 GMC that sat for at least 4 yrs. It was the first time I drove it & when I pulled into the driveway smoke was coming out from under the hood. I had an old 69 Chevy harness that I had to alter a little to make work. So far no issues but I plan on buying a new harness pretty soon. Take a look!

[70 Long Fleetside]

Exactly what mine looks like. I'll post a pic tomorrow. Thanks!

[Raider Rudy]

Originally Posted by 70 Long Fleetside

Exactly what mine looks like. I'll post a pic tomorrow. Thanks!

Im not good with electrical, but my buddy up thd street took a look and said it was missing the fuseable link.

[70 Long Fleetside]

Even if the link saved the harness it would be a challenge to find the real issue. The rewire looked awful when I bought it, dead wires all over under the dash and hood, and the reverse lights stayed on with the key off, and a viper security unit that didn't work. I knew I needed to go through it but I didn't know where to start. I only put about 2000 miles a year on it so I never had the motivation to go through it. Now I have to and I'll at least know what I've done and I'll learn something.
I'll ask questions when I need help and let you know what I figure out.
Thanks again

[snipescastle2]

I have a second front light harness off of a '71-'72 you're welcome to it, if you like, just pay the shipping......
Ben

[70 Long Fleetside]

Thanks man, I ordered a full harness. I appreciate the offer.

[70 Long Fleetside]

didn't take as long as I thought. The short in the wiring board for the instrument panel might be be culprit. Any thoughts?

[70 Long Fleetside]

Glad that's done!

[70 Long Fleetside]

The temp gauge failed a couple weeks ago and then the gas gauge. So if that happens to you...
Would have been a really easy fix.
I don't know why they didn't line the back of the panel. It only lasted 45 years!