LMC Heavy-Duty Headlight Harness Review:

[Greasey Harley]

I recently installed an LMC Headlight Relay Harness in my '79 K10. It is the same part for 67-72 GM Trucks with 2 headlights.
LMC Part Number: 36-3580
https://www.lmctruck.com/1973-87-che...dlight-harness

$45 shipped to my door, and proudly manufactured in Taiwan ROC.
It seems reasonably well made and all the connections are good. It came with plastic sheathing wire protector, that I had to split with a razor knife,so that I could remove it. I chose to run it thru the factory split loom (personal preference). also it seemed to fit the truck better that way.
The harness fit decently, however, the blue and yellow wires that go across the radiator, to power the Drivers side headlight, should be a few inches longer (IMHO). I plan on lengthening them, as there is virtually no slack between the relays and the Driver's Headlight. You can see the wires pulled tight in the pic, they show just across the top corner of the battery. You may also note that the relays don't hang straight, this is also due to the driver's headlight wires being slightly too short.
The only other issue that I had was that there is no fuse supplied, between Battery + and the relays. To resolve this, I installed a cheap Amazon Aux Fuse Block: https://www.amazon.com/Warning-Indic...672067&sr=8-17



As far as performance, there was a noticeable difference, but not a dramatic one. I recently replaced all my headlight components and cleaned/replaced every ground under my hood. I believe that if this harness was installed on a truck with dirty grounds and old components, the difference would be dramatic. I have no scientifical way to measure the difference, however, I am sure, there was definitely an improvement over the factory lighting system, all be it a modest one.

For what it's worth,
-Russ

[Andy4639]

Nice work. Looks good sir.


I did my own relay upgrade for about $20.00. I used a car audio fuse holder by the battery with a 40amp fuse.
My lights where good but not great.

I checked the voltage before and after the install.

Before I was getting about 11 volts to the drivers side head light afterwards it was 13 volts. This was with the motor running at idle.

[Greasey Harley]

Originally Posted by Andy4639

Nice work. Looks good sir.


I did my own relay upgrade for about $20.00. I used a car audio fuse holder by the battery with a 40amp fuse.
My lights where good but not great.

I checked the voltage before and after the install.

Before I was getting about 11 volts to the drivers side head light afterwards it was 13 volts. This was with the motor running at idle.

Thing is, I have clean battery voltage coming out of both harnesses. Like virtually identical. However, There is almost certainly less resistance through the aftermarket harness ...right?? [whatever]

Anyways, how much too short was the LMC harness? 'bout this much:


,and would you believe, I still didn't have the right color of blue?


I hate cutting up a new harness, but wires gotta lay proper! chop-chop


I think I'll build my own harness for my '68.
-Russ

[toolboxchev]

I cleaned all my grounds, everywhere! Fixed all potential wiring issues on an ongoing basis soldering connections where possible.

Noticed the headlights do not dim very much anymore especially when in gear, with all the other electrical running.

Not known if I would do this without modernizing much more of the electrical. Everything on my truck is mostly stock electrically, alt, volt reg, with the exception of a HEI.

[Andy4639]

With a newer wiring harness you should have about the same. I'm still using the original harness in all my trucks & cars. I have built all my own head light relay kits for them. I have a 56 Bel Air, 64 SS Impala, 67 c-20, 68 c 10 and my 71 C 10. They all have the factory wiring except the 56 it has a newer harness in it but I added the relays.

Yea chopping up a new harness isn't fun but it has to be done sometimes though.

[gmachinz]

Overseas wiring “manufacturers” use a good amount of tin filler metal instead of pure copper wiring-much cheaper for them and 99.9% of customers won’t ever know. The result is tin has a poor rate of electrical resistance which adds heat to the circuit-the longer its on, the more heat gets generated. Also, the wire jacketing is not j1128 rated for underhood engine temps. But again, 99.9% of people don’t know this so thats why they hope cheap sells.

[toolboxchev]

Just had the external wiring for a HEI dist. crack on me. The product is 9 years old. Took out an Accel Supercoil, HEI Module, all over a 10 dollar part.

See it.

[gmachinz]

Yep-that’s Asian wiring for ya!

[Andy4639]

Originally Posted by toolboxchev

Just had the external wiring for a HEI dist. crack on me. The product is 9 years old. Took out an Accel Supercoil, HEI Module, all over a 10 dollar part.

See it.

Is this some kind of kit you bought are is it just newer wires you installed? Just wondering.

This is why I like my old stock harness. The product is solid and no worries of amps going through it.

[gmachinz]

The problem is overseas manufacturing doesnt adhere to the same quaity as OEM when it comes to components. Brass plated tin terminals for example vs zinc coated copper like OE Delphi, tin filler metal added to copper for wiring strands, acrylic jacketed wiring vs j1128 rated SXL material, etc. Every corner that can be cut has been cut because the consumer overall outs price ahead of quality at the end of the day. I’ve always felt high quality parts aren’t expensive, it’s just have over the last 25+ years have gotten used to cheap prices w/o any thought to the degradation of quality work. How does one go back to it?

[Dead Parrot]

I installed one of these harnesses on my CUCV. It is a recommended installation over on the Steel Soldiers forum. Apparently on the CUCV's all the normal civilian circuits run through one 30A fuse and wire and overheating is common. Moving the many amps of headlight draw off that circuit mostly eliminates the problem.

I had replaced the 2 post J-block with one of the many post versions off a 90's era truck. Got my power from that by using one of the salvaged OEM made fusible links to protect the relay setup. Also avoids having random wires being ran to a battery post.

The harness replaced one of the OEM sockets that had an intermittent failure. Guessing corrosion but that one is hard to get to on a CUCV.

So far, results are good.

[RustyPile]

Originally Posted by Greasey Harley

The harness fit decently, however, the blue and yellow wires that go across the radiator, to power the Drivers side headlight, should be a few inches longer (IMHO). I plan on lengthening them, as there is virtually no slack between the relays and the Driver's Headlight. You can see the wires pulled tight in the pic, they show just across the top corner of the battery. You may also note that the relays don't hang straight, this is also due to the driver's headlight wires being slightly too short.

Why not just locate the relays closer together????? Make trial fitting before final fitting/assembly your new best friend..

[gmachinz]

See that’s why LMC’ kit just isnt designed well. My kits I pull power directly off the firewall common junction (which is fed a 10ga charge wire via the alt charge post) and I use a sealed style 30A fuse ahead of the relay bank which mounts near the drivers side headlight on the core support or fender. Then the RH side leads route inside the OE loom and extend over that way. Heck on underdash/fuse panel assemblies I’ve started integrating the headlight relays into the OEM style harness so there are no relays underhood for this mod.

[Greasey Harley]

Originally Posted by RustyPile

Why not just locate the relays closer together????? Make trial fitting before final fitting/assembly your new best friend..

They just seemed to fit better there.
Like I said, I'll probably build a harness for my '68, from scratch.

Funny story about how dumb I am:
I got that harness done and friggin' HATED that big ugly yellow butt connector going to the aux fuse block, and decided a Weather-Pack connector would look better.
So, I bought: 10ea- 10awg Weather Pack connectors and a pair of crimpers for $85.
...Well that seems expensive for one connector, plus the crimpers only fit 12-10awg wire. So what is my brilliant solution?
I bought:
Crimpers for the smaller wires
10ea: 2 plug W-P connectors
10ea: 3 plug W-P connectors
10ea: 4 plug W-P connectors
seals and terminals for 18-20awg 16-14awg and 12-10awg ...I lost count

Total, I spent about 235 bucks on weather-pack connectors, just because I hate butt connectors. All that money and I have completed exactly one conection

Here's a pic of my boondoggle:


Looks $235 worth of better to me
-Russ

[Andy4639]

You don't have to run the hot wire to the battery guy's. You can take the hot from the back of the alternator are out of the drivers side loom where the hot junction is in the factory wiring. It's right there on the radiator support by the drivers side head light.