lmc HD headlight harness gmc/4 lights

[C5Phil]

OK... I have the same lmc harness with the same issue (dim lit blubs on sometimes) on my GMC... I tried to follow this thread but got confused real quick-- the way I read through it there seems to be posted multiple solutions...Am I wrong? in any case I can't follow any of them (yes I'm electrically illiterate) could someone give me simple step by step instructions on how to install the screwed up LMC harness in to my 70 GMC? i'd be forever grateful.....
And I bet this would make a great sticky in the FAQ section--

[chalet2506]

Dredging this one up. Didn't realize this harness was such a pita when I ordered it, but figure I might as well make it work.

1st thing. Its been about a year and a half since I drove the truck and I don't remember how the oe headlights work. Inside and outside bulds lit up on bright, and outside only on dim?

C5phil did you figure it out? I have the same problem. I went with custom dashes and don't have a high beam indicator hooked up yet. Matched the wire color positions on the plug from the oe harness to the LMC Harness. But 1st switch position I had everything lit up. 2nd switch position I got bright outside(3 prong bulb) and very dim inside lights.

So driver side I moved the green / brown wires on the the 3 prong bulb on driver side to match the color position on the original plug. Now on that side I have everything lit up in 1st position still, but dim and very dim on 2nd switch position.

Truck is a 72 GMC Jimmy

[C5Phil]

Originally Posted by chalet2506

Dredging this one up. Didn't realize this harness was such a pita when I ordered it, but figure I might as well make it work.

1st thing. Its been about a year and a half since I drove the truck and I don't remember how the oe headlights work. Inside and outside bulds lit up on bright, and outside only on dim?

C5phil did you figure it out? I have the same problem. I went with custom dashes and don't have a high beam indicator hooked up yet. Matched the wire color positions on the plug from the oe harness to the LMC Harness. But 1st switch position I had everything lit up. 2nd switch position I got bright outside(3 prong bulb) and very dim inside lights.

So driver side I moved the green / brown wires on the the 3 prong bulb on driver side to match the color position on the original plug. Now on that side I have everything lit up in 1st position still, but dim and very dim on 2nd switch position.

Truck is a 72 GMC Jimmy

i hate to be a downer-- but I tried and tried to fix my LMC harness never could getit correct-- I have limited electrical knowledge- so I ended up going with a harness from these guys--

http://67-72chevytrucks.com/vboard/s...d.php?t=535233


never been happier- works like a charm and was a perfect plug and play- LMC just kept giving me the run around- even sent me another harness- it functioned the same as the old one- like crap!!! Hope you get your lights sorted out -- Good Luck

[C5Phil]

PS. as referenced in my previous post-- Anyone want to buy a brand new in the original packing LMC heavy duty headlight harness for a GMC? LOL

[GMCJOE]

Originally Posted by C5Phil

PS. as referenced in my previous post-- Anyone want to buy a brand new in the original packing LMC heavy duty headlight harness for a GMC? LOL

I pay the shipping if you want you just want to give it away...

[davepl]

In my case I just popped ALL the connections out of the headlight style connectors on the harness and redid them by following the factory color scheme. The harness has green and brown wires, as does the factory harness.

Basically one of your factory harness green wires winds up triggering a relay that powers all the green wires, which in turn connect to the headlights where the original green wires did. Same deal for the brown. I followed that basic rule and it all worked first time when I reconnected everything.

[chalet2506]

Thanks. I'll give that a try.

[chalet2506]

Originally Posted by davepl

In my case I just popped ALL the connections out of the headlight style connectors on the harness and redid them by following the factory color scheme. The harness has green and brown wires, as does the factory harness.

Basically one of your factory harness green wires winds up triggering a relay that powers all the green wires, which in turn connect to the headlights where the original green wires did. Same deal for the brown. I followed that basic rule and it all worked first time when I reconnected everything.

That did it. Just make sure get the ground on the correct side of the three prong plug. I didn't figure it mattered and still had just enough power bleed into the high beam, 2 prong lamp on dim to make the filament turn orange.


Don't know why that is, but electrical isn't my thing.

Only problem is the 90 deg spades don't fit correctly into the plug now. Not a big deal, but the whole mess is a little irritating.



Thanks for the help.

[C5Phil]

Originally Posted by chalet2506

That did it. Just make sure get the ground on the correct side of the three prong plug. I didn't figure it mattered and still had just enough power bleed into the high beam, 2 prong lamp on dim to make the filament turn orange.


Don't know why that is, but electrical isn't my thing.

Only problem is the 90 deg spades don't fit correctly into the plug now. Not a big deal, but the whole mess is a little irritating.



Thanks for the help.

The ground position must have been my problem- I didn't think it mattered either- but I gave up- to soon it looks like--

[GMCJOE]

Originally Posted by davepl

In my case I just popped ALL the connections out of the headlight style connectors on the harness and redid them by following the factory color scheme. The harness has green and brown wires, as does the factory harness.

Basically one of your factory harness green wires winds up triggering a relay that powers all the green wires, which in turn connect to the headlights where the original green wires did. Same deal for the brown. I followed that basic rule and it all worked first time when I reconnected everything.

So you are saying just on the headlight side of the LMC harness you have to match up the wires to the factory harness? Nothing else required at the relay's or where you plug the power side of the factory harness into the LMC harness?

[chalet2506]

Originally Posted by GMCJOE

So you are saying just on the headlight side of the LMC harness you have to match up the wires to the factory harness? Nothing else required at the relay's or where you plug the power side of the factory harness into the LMC harness?

I changed the headlight plugs and the plug that connects to the factory wire harness.

The upside about having to deal with this is I now have a pretty good idea how the headlight system works. If there are any more problems down the road I'll just toss the lmc harness and build my own.

Might end up doing that anyway, having all the original headlight plugs and wires hanging around looks kind of junky.

[Square_78]

Sounds like a nightmare. Hopefully LMC corrects this problem.

[GMCJOE]

Thanks.. I figured if you did the head light connectors, the harness end would have to be done too. I figured they had at least wired the relay's right, since they will only work right in one configuration. I understand the principles off electricity, but I hate dealing with it cause I still haven't quite got down wiring up relay's yet. And being a mechanic in the Army, they have trained me on it a couple times. Mostly on trouble shooting a electrical system with relay's, and one class building a high beam low beam light system on a electrical board. Talk about sucking something fierce at it...lol Understanding the concept of a relay isn't hard though.

I bought C5Phil's extra LMC HD Light harness for my future switch to the H5 headlights on my GMC, figured it would save me a few dollars and get some hands on electrical training again.

And I very seriously doubt LMC will correct this issue, considering they purchase the product from someone else. To them it's not the product that has an issue. Maybe if enough people complain that purchase it, they will find another company to go thru. So far I haven't had any issues with anything I have purchase thru them.

[DDassow01]

I know this is an old thread but it helped me with the LMC HD Headlight wiring harness on my 70 GMC. It is still wired wrong but I was able to remove the connections from the wiring harness sockets and match them up with the factory wiring and it worked just fine. Here is the harness as it came from LMC...

[DDassow01]

And here is how it should be wired. There is also a picture of the low beam connection that had to be modified on both sides to match up with how the factory wiring was. Kind of a pain to have to modify something new out the box but once done it works great and looks good. Lights are noticeably brighter now.