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Old 06-30-2019, 12:45 PM   #1
bluec10
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LMC Heavy Duty Headlight Wiring Harness

Just installed LMC’s Heavy Duty Headlight Wiring Harness. The install went well except for one of the ground wires was too short - easy fix. When I turned on the headlights I found that the high beams worked fine, but I have no low beams. Anyone familiar with this setup? Advice to solve the problem?
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Old 06-30-2019, 12:50 PM   #2
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Re: LMC Heavy Duty Headlight Wiring Harness

try switching the relays to see if you got lows and no high if so its a bad relay if not going to have to check wire harness
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Old 06-30-2019, 02:37 PM   #3
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Re: LMC Heavy Duty Headlight Wiring Harness

I bought on on ebay for $20 for my gmc had no problems.
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Old 06-30-2019, 05:52 PM   #4
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Re: LMC Heavy Duty Headlight Wiring Harness

Make sure the relays are not swapped one should be a 4 prong other should be 5 prong relay. I had the same problem .
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Old 06-30-2019, 06:12 PM   #5
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Re: LMC Heavy Duty Headlight Wiring Harness

And don't forget a fuse for them, if you haven't put one in already.
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Old 07-01-2019, 03:24 PM   #6
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Re: LMC Heavy Duty Headlight Wiring Harness

Thanks for the advice. I hadn’t thought of the relays.
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Present:
2015 Tacoma. Yeah, not a GM, but I love it.
1969 GMC 32,000 - fix, drive, relax, fix...
2019 BMW R1250 GSA - Yahoooooooo
1979 Honda GL 1000 - retro touring at its best.

Past:
'05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner.
'94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm.
'79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350.
'76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod.
'68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect.
'59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.
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Old 07-01-2019, 07:56 PM   #7
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Re: LMC Heavy Duty Headlight Wiring Harness

The relays are identical. Both of the plugs that go into the relays have 4 plugs.
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Present:
2015 Tacoma. Yeah, not a GM, but I love it.
1969 GMC 32,000 - fix, drive, relax, fix...
2019 BMW R1250 GSA - Yahoooooooo
1979 Honda GL 1000 - retro touring at its best.

Past:
'05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner.
'94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm.
'79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350.
'76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod.
'68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect.
'59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.
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Old 07-02-2019, 09:57 PM   #8
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Re: LMC Heavy Duty Headlight Wiring Harness

mine is from lmc also it has only 4 on both . the extra pin is for a normally closed circuit . you shouldn't need the extra pin because you have a dimmer switch that feeds power to one relay or the other . if it is wired correctly it wouldn't matter if you used a 4 pin or 5 pin relay the connector wouldn't have a wire for the pin so either would work as long as it was rated for the same amperage
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Old 07-02-2019, 10:48 PM   #9
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Re: LMC Heavy Duty Headlight Wiring Harness

Quote:
Originally Posted by Warrens69GMC View Post
And don't forget a fuse for them, if you haven't put one in already.
I installed this kit recently. I went and looked, and discovered it does not have fuses. I'll be adding fuses into the circuits. Good info!
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Old 07-15-2019, 12:32 PM   #10
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Re: LMC Heavy Duty Headlight Wiring Harness

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Originally Posted by Steeveedee View Post
I installed this kit recently. I went and looked, and discovered it does not have fuses. I'll be adding fuses into the circuits. Good info!
I installed this kit into my GMC this weekend. I’m curious as to
where in the circuit I should install the fuses and what rating fuses would be appropriate. Thanks!

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Old 07-15-2019, 02:30 PM   #11
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Re: LMC Heavy Duty Headlight Wiring Harness

Wrote out a long post that didn't post. shorter version...

Test the power coming out of the head light switch. Test each of the inputs to the relays. Swap relays to see if the problem follows the relay. If you remove and reinstall the relays while the headlights are on, you should hear the relay click as power is applied.

Fuses, I like to install as close to the battery or junction as possible. Headlights should draw around 10A. 15-20A should be good.
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Old 07-15-2019, 03:03 PM   #12
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Re: LMC Heavy Duty Headlight Wiring Harness

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Originally Posted by rpmerf View Post
Wrote out a long post that didn't post. shorter version...


Fuses, I like to install as close to the battery or junction as possible. Headlights should draw around 10A. 15-20A should be good.
Thank you rpmerf! That is what I was thinking, but it never hurts to get an expert opinion.
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Old 07-15-2019, 06:43 PM   #13
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Re: LMC Heavy Duty Headlight Wiring Harness

Just got back to this thread. I haven't put any fuses in yet, since I have been doing other things. Thanks rpmerf for the information!
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