LMC Heavy Duty Headlight Wiring Harness - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 06-30-2019, 12:45 PM

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?

firedemon · 06-30-2019, 12:50 PM

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

71gmcC15 · 06-30-2019, 02:37 PM

I bought on on ebay for $20 for my gmc had no problems.

**Hidesertchevy** · 06-30-2019, 05:52 PM

Make sure the relays are not swapped one should be a 4 prong other should be 5 prong relay. I had the same problem .

**Warrens69GMC** · 06-30-2019, 06:12 PM

And don't forget a fuse for them, if you haven't put one in already.

bluec10 · 07-01-2019, 03:24 PM

Thanks for the advice. I hadn’t thought of the relays.

bluec10 · 07-01-2019, 07:56 PM

The relays are identical. Both of the plugs that go into the relays have 4 plugs.

firedemon · 07-02-2019, 09:57 PM

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

**Steeveedee** · 07-02-2019, 10:48 PM

Quote:

Originally Posted by Warrens69GMC

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!

Chuck A · 07-15-2019, 12:32 PM

Quote:

Originally Posted by Steeveedee

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!

rpmerf · 07-15-2019, 02:30 PM

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.

Chuck A · 07-15-2019, 03:03 PM

Quote:

Originally Posted by rpmerf

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.

**Steeveedee** · 07-15-2019, 06:43 PM

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!

06-30-2019, 12:45 PM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	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? __________________ 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.

06-30-2019, 12:50 PM	#2
firedemon Registered User Join Date: Jun 2015 Location: @ Posts: 890	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

06-30-2019, 02:37 PM	#3
71gmcC15 Registered User Join Date: Feb 2018 Location: Doland SD Posts: 836	Re: LMC Heavy Duty Headlight Wiring Harness I bought on on ebay for $20 for my gmc had no problems. __________________ ( second times the charm) 71 gmc c15 307 sbc 373 rear gears positrac sm 465 trans. ( not listed on spid but is original ) 94 chevy k1500 350 tbi 373 rear gears 4l60e one wheel peel. Gutless 07 gmc sierra classic rcsb 4.3 lt 5 speed w/t 04 chevy Silverado 1500 ext cab 5.3 4l60e. 81 chevy Scottsdale k10 muncie sm465 Np208 10 bolt 8.2 ( Old Green)

06-30-2019, 05:52 PM	#4
Hidesertchevy Senior Member Join Date: Mar 2017 Location: yucca valley Posts: 271	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 .

06-30-2019, 06:12 PM	#5
Warrens69GMC Registered User Join Date: Jan 2003 Location: Safford,AZ Posts: 3,625	Re: LMC Heavy Duty Headlight Wiring Harness And don't forget a fuse for them, if you haven't put one in already. __________________ 1969 307, t350 1950 Chevy Wagon 1978 Big 10 1967 C10, 250,3-OTT

07-01-2019, 03:24 PM	#6
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Re: LMC Heavy Duty Headlight Wiring Harness Thanks for the advice. I hadn’t thought of the relays. __________________ 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.

07-01-2019, 07:56 PM	#7
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Re: LMC Heavy Duty Headlight Wiring Harness The relays are identical. Both of the plugs that go into the relays have 4 plugs. __________________ 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.

07-02-2019, 09:57 PM	#8
firedemon Registered User Join Date: Jun 2015 Location: @ Posts: 890	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

07-15-2019, 02:30 PM	#11
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	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. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

07-15-2019, 06:43 PM	#13
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,708	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! __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

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