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Old 09-14-2018, 09:16 PM   #1
HIGHWAY BY THE SEA
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No lights work

This 67 GMC 3500 of mine does not have a working light system. Even the cab interior light does not work. I am leaning toward a new lighting system wiring harness, but am wondering what I may be overlooking. I have checked the wires under the hood, and they seem ok. There are NO junction blocks, so perhaps a hidden fusible link?
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1981 Chevrolet C10 Deluxe Shortbed Stepside
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http://67-72chevytrucks.com/vboard/s...d.php?t=584617
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1967 GMC 3500 dually one-ton flatbed
http://67-72chevytrucks.com/vboard/s...d.php?t=770578
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Old 09-15-2018, 05:15 PM   #2
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Re: No lights work

Quote:
Originally Posted by HIGHWAY BY THE SEA View Post
This 67 GMC 3500 of mine does not have a working light system. Even the cab interior light does not work. I am leaning toward a new lighting system wiring harness, but am wondering what I may be overlooking. I have checked the wires under the hood, and they seem ok. There are NO junction blocks, so perhaps a hidden fusible link?

Does it start and run? Do you have power to the headlight switch or the turn signal switch? The fusible link is the short wire between the + battery terminal and the junction block on the passenger inner fender. Do you have power at the junction block?

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Old 09-15-2018, 08:48 PM   #3
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Re: No lights work

There should be a smaller wire from the + batt terminal and then a fusible link to a junction block on the pass fender. That's what feeds everything but the starter motor. If it runs, then someone got creative with the wiring and it's time to get out the voltmeter.
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Old 09-16-2018, 09:42 PM   #4
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Re: No lights work

The red wire in the firewall connector seems to be the problem. I GUTTED the lighting wire harness today, and it snapped loose from the firewall plug in my hand. This truck has no junction box either. It does not run at this time but it turns over and over. I'm about to put an HEI distributor in there and I believe that will get it running. I have decided to buy a new lighting harness from LMC. This one has several exposed wires throughout it and they do not look very good. I was not able to see how bad it was until I tore it out of there today.
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1981 Chevrolet C10 Deluxe Shortbed Stepside
GRANDTRUCK
1968 Chevrolet C10 Stepside Longbed
http://67-72chevytrucks.com/vboard/s...d.php?t=584617
NEW PROJECT
1967 GMC 3500 dually one-ton flatbed
http://67-72chevytrucks.com/vboard/s...d.php?t=770578
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Old 09-16-2018, 09:44 PM   #5
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Re: No lights work

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Originally Posted by HIGHWAY BY THE SEA View Post
The red wire in the firewall connector seems to be the problem. I GUTTED the lighting wire harness today, and it snapped loose from the firewall plug in my hand. This truck has no junction box either. It does not run at this time but it turns over and over. I'm about to put an HEI distributor in there and I believe that will get it running. I have decided to buy a new lighting harness from LMC. This one has several exposed wires throughout it and they do not look very good. I was not able to see how bad it was until I tore it out of there today.

That might be the best course of action at this point. Let us know how it goes....

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Old 09-19-2018, 11:05 AM   #6
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Re: No lights work

After dealing with this wiring issue, I am considering going with the HEI, matching wiring harness, and an internally regulated alternator. I wonder if I should hook up some junction blocks too...?
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http://67-72chevytrucks.com/vboard/s...d.php?t=584617
NEW PROJECT
1967 GMC 3500 dually one-ton flatbed
http://67-72chevytrucks.com/vboard/s...d.php?t=770578
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Old 09-19-2018, 11:58 AM   #7
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Re: No lights work

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Originally Posted by HIGHWAY BY THE SEA View Post
After dealing with this wiring issue, I am considering going with the HEI, matching wiring harness, and an internally regulated alternator. I wonder if I should hook up some junction blocks too...?

I can't advise on that. I think VetteVet added a junction block where the three red power wires connect up by where the voltage regulator was....


Read this thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=757426

It pretty much explains everything on that.

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Old 09-19-2018, 02:35 PM   #8
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Re: No lights work

Quote:
Originally Posted by HIGHWAY BY THE SEA View Post
The red wire in the firewall connector seems to be the problem. I GUTTED the lighting wire harness today, and it snapped loose from the firewall plug in my hand. This truck has no junction box either. It does not run at this time but it turns over and over. I'm about to put an HEI distributor in there and I believe that will get it running. I have decided to buy a new lighting harness from LMC. This one has several exposed wires throughout it and they do not look very good. I was not able to see how bad it was until I tore it out of there today.
You haven't been paying attention. Read on this forum about people's bad experiences with LMC. There are much better suppliers out there. Two of the best sources for parts for these pickups for things you can't buy at your locally-owned parts store are classicheartbeat.com and gmcpauls.com. I know Classic Heartbeat has things available that are not on their website. For wiring harnesses, there are lots of good sources out there like Painless Performance, American Autowire and others.
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Old 09-19-2018, 03:34 PM   #9
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Re: No lights work

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Originally Posted by TheRocket View Post
You haven't been paying attention. Read on this forum about people's bad experiences with LMC. There are much better suppliers out there. Two of the best sources for parts for these pickups for things you can't buy at your locally-owned parts store are classicheartbeat.com and gmcpauls.com. I know Classic Heartbeat has things available that are not on their website. For wiring harnesses, there are lots of good sources out there like Painless Performance, American Autowire and others.
Classic sells M&H or American Autowire....They can tailor as needed, such as for HEI, internally regulated alternator, etc.

Some notes on the red wire OP:

Three wires attach to junction block secured with a 3/8" flange nut for a #10-24 stud. The three wires are described as:

• 12 AWG red: This wire runs to the positive terminal on the battery.

• 12 AWG red & fusible links configuration: A 12 AWG red wire runs from the firewall block to a splice. This wire is soldered with three additional 12 AWG red wires. One wire routes to the alternator, one wire to the voltage regulator, and one wire to a fusible link that attaches to the junction block. NOTE: The red wire from the firewall block also uses a fusible link near the splice.

• 18 AWG black: This wire connects to #12 on the cluster connector and then down to the fuse box. It then runs from firewall block to the junction block. This wire has a 4 AMP in-line fuse near the junction block.
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Last edited by 71CHEVYSHORTBED402; 09-19-2018 at 03:56 PM. Reason: Red wire
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Old 09-20-2018, 11:51 AM   #10
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Re: No lights work

Thanks for all the helpful information about wiring harnesses and where NOT to buy them. The 67 chevy front clip that I am buying has SOME type of wiring harness in it, but I'm not sure if it is the lighting/alternator harness, or the engine harness. I will find this out on pickup day.
What I would really like to do is convert this to HEI (with GMC Paul's harness), and install an internally regulated alternator. That should eliminate the need for that black box under the washer bottle I believe. I have to figure out which harness will be correct for this since this conversion strays away from 67 factory specs.
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1981 Chevrolet C10 Deluxe Shortbed Stepside
GRANDTRUCK
1968 Chevrolet C10 Stepside Longbed
http://67-72chevytrucks.com/vboard/s...d.php?t=584617
NEW PROJECT
1967 GMC 3500 dually one-ton flatbed
http://67-72chevytrucks.com/vboard/s...d.php?t=770578
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