Head lamp Issues

[mygmctruck1]

This has me baffled.

I installed a premade LMC head lamp harness with relays for my new h4 head lamps.

The lights works fine before the install.

on low beams , the low beam is bright as it should be but the high beam is on also but dim ? Then if I switch to HIGN beam , the hi beam is bright as is should be and the low beam lamp is dim and it shouldn't be ?
In other words on low beams the high beam shouldn't be on at all but on H Beams both should be on bright but the low beam is dim.

What the H*** is going on ?

Cross wire ?

[truckster]

I would bet you're missing a ground wire.

[michael bustamante]

yup run another ground from the rad support to the frame

[Sheepdip]

Yep.... 90% of electrical problems are grounding issues.

[mygmctruck1]

Bad ground is the first thing I checked. I grounded right to the battery.
So then I thought maybe bleed over in dimmer switch , No not that either.

So I tested both low and hi beam wires separately , No bleed over . On low beam no power bleed over at Hi beam and on Hi beam , no power bleed over at low beam wire. using a testor.
It's got to be in the harness some where .

Like I mentioned earlier , prior to the new H4 harness , everything worked fine grounding as should be.

[Ol Blue K20]

I still think it's a ground problem. It sounds.like its trying to use the high beams for a ground.

[mygmctruck1]

Originally Posted by Ol Blue K20

I still think it's a ground problem. It sounds.like its trying to use the high beams for a ground.

Well , I am inclined to agree it's a ground issue , except prior to the new wring harness from LMC , My lights worked as they should. When I installed new harness , I grounded the harness / lights to the same grounding points .

I pulled the harness and hooked up my original harness with original grounding points and guess what they work as they should.

I hate 12 volt systems.

[Fbks_Cruiser]

I think you may have found your problem: "installed a premade LMC head lamp harness"

Sound like it may have a break within it's ground circuit. Test the continuity within the ground legs of the LMC harness.

[mygmctruck1]

Originally Posted by Fbks_Cruiser

I think you may have found your problem: "installed a premade LMC head lamp harness"

Sound like it may have a break within it's ground circuit. Test the continuity within the ground legs of the LMC harness.

Well I’ll try that , we’ll see

[rockyrivermark]

Typical LMC crap parts. I wouldn’t buy a license plate frame from them.
Garbage parts

[Andy4639]

There are post about the LMC head light relay harness having problems in the past. Do a search on here to find the links about it.
Wires crossed up all kinds of stuff.

[mygmctruck1]

Originally Posted by Andy4639

There are post about the LMC head light relay harness having problems in the past. Do a search on here to find the links about it.
Wires crossed up all kinds of stuff.

Thank you , what an eye opener. I should have guessed , not all my experience with LMC has been bad . But they haven’t a clue about anything except sales !

[Ben IV]

I just installed one the other day with the same issue. I thought it was odd that the harness only tied into the factory low beam plug and nothing into the factory high beam plug which could have something to do with it.

I am very mechanically inclined but shy away from wiring but I guess I need to just install relays into the factory harness.

[mygmctruck1]

Originally Posted by Ben IV

I just installed one the other day with the same issue. I thought it was odd that the harness only tied into the factory low beam plug and nothing into the factory high beam plug which could have something to do with it.

I am very mechanically inclined but shy away from wiring but I guess I need to just install relays into the factory harness.

What an who’s unit did you get ? If you have only 2 head lamps , you only have one plug . Actually one plug for a 4 lamp set too.

[Andy4639]

It's a pretty easy upgrade really.

Take a test light and pull the head light connector off the drivers side light.
With the test light on one of the contacts figure which wires are which...High/low.
The drivers side connector works both lights.

Then cut them about 12" away form the light.
Take the end from the harness and this will be your trigger wire for the relay # 86 in the picture to the H beam one you are doing. Then the end to the head light goes to #87.
You can run a #10 are #8 wire from the battery for the hot wire to the relays # 30 on both with inline fuse.
Then ground each relay #85 to a good ground close to the relay.
Repeat this for both relays.
There is no use in using 4 relays for the GMC truck's, 2 relays will handle both lights easy.

[Ben IV]

Originally Posted by mygmctruck1

What an who’s unit did you get ? If you have only 2 head lamps , you only have one plug . Actually one plug for a 4 lamp set too.

Lmc kit on my 70 gmc.

[mygmctruck1]

Well the problem is fixed, The solution came when I read an old post by
Irishbleueyes and others on this site. We have awesome people on this Forum !
He ran into the same problem and found the wiring to the low/high beam head lamp was back wards. I used my AAW wiring diagram to rewire the 3 prong plugs . Bingo everything works correctly.

So if you have the LMC harness , more than likely , it's wired wrong. Lmc , sent me a brand new one because I *****ed. But of course it's also wired wrong

[Fbks_Cruiser]

Good deal. Thanks for letting us know what the fix was.

[Boog]

This is good to know now. I bought one of their kits a while back but haven't yet installed it. I'll be looking for this issue. Thank you.

[EagleChief]

Interesting. I need to check mine. I did run into an issue with the kit. After sitting over the winter, my brand new battery was drained (started only a few times over the cold spell), and the wiring on the LMC harness was split in places and had the electrical crud buildup (like you see on the battery terminal posts) coming out of the wiring.

I cleaned it up the best I could and haven't had an issue since. But, I'm thinking I need to take it off of the truck and try something else.

I need to look at the lights when they are on and see if I'm having the same issue.

[mygmctruck1]

Originally Posted by EagleChief

Interesting. I need to check mine. I did run into an issue with the kit. After sitting over the winter, my brand new battery was drained (started only a few times over the cold spell), and the wiring on the LMC harness was split in places and had the electrical crud buildup (like you see on the battery terminal posts) coming out of the wiring.

I cleaned it up the best I could and haven't had an issue since. But, I'm thinking I need to take it off of the truck and try something else.

I need to look at the lights when they are on and see if I'm having the same issue.

Another good reason to disconnect battery durning long periods of down time .

[mygmctruck1]

Ok here what I did to the LMC wiring harness.
Looking at the back of the 3 prong plug , the left pic is the correct wiring and the diagram on the right is how the LMC harness is wired .
The Bl or ( gr ) wire goes in the left slot
The Tan / Brown low beam goes in the top center slot
The Green Hi beam goes in the right slot .

This applies to both plugs for the Low / Hi beam plug , The high beam only plug does not change.

As you can see LMC’s harness is WRONG but being from China I am not surprised .

[Steeveedee]

Originally Posted by EagleChief

Interesting. I need to check mine. I did run into an issue with the kit. After sitting over the winter, my brand new battery was drained (started only a few times over the cold spell), and the wiring on the LMC harness was split in places and had the electrical crud buildup (like you see on the battery terminal posts) coming out of the wiring.

I cleaned it up the best I could and haven't had an issue since. But, I'm thinking I need to take it off of the truck and try something else.

I need to look at the lights when they are on and see if I'm having the same issue.

Now that is interesting, because my truck's battery was low the other day. There's a small drain somewhere and maybe it's those relays. I'll have to check that out. It's pretty new kit; I'll look for corrosion on mine.