Headlight Harness Install

[72SB]

I am sure several have done this but I just installed the LMC harness on my 72. Did same thing in my 67 Camaro last year.

The harness relieves the full 12v load from headlights away from the headlight switch making not only any headlight bulb you use brighter but also all the other lights, including dash lights. The headlight switch now just triggers relays that connect +12VDC from battery + terminal buss on PS fender.

Install is plug & play. No cutting any stock wires. I just put a larger O ring crimp on one of the ground wires for the kit because the existing bolt location for another ground required a larger crimp eyelet. No big deal.

For those who have not done this, its a simple, good mod which improves light output. I installed Sylvania Silver Star Halogen headlights in the higher color temp version so the headlights look more like modern cars in terms of brightness and color temp but otherwise are same watt load as stock.

[Chevys4life]

Thanks for the informaion headlight upgrade harness. I am going to look into it for my truck. What is name of the harness on in the LMC catalog?

[Steeveedee]

Nice, clean installation!

[72SB]

Originally Posted by Chevys4life

What is name of the harness on in the LMC catalog?

36-3580 HEAVY-DUTY HEADLIGHT HARNESS

https://www.lmctruck.com/1973-87-che...dlight-harness

scroll down too vehicle application

it was a plug and play install. I ran the harness under core support so did remove the radiator brackets to get the plug end between radiator and core support. I used existing holes in core support to zip tie the harness under it

Only holes I drilled was to secure the two relays. You could mount then elsewhere but are limited to the length of wire as to where. Basically, around the battery area or front or rear of core support. I chose my location for ease of replacing the relay should I ever need to but mounting them between battery and core support would be another option if you did not want to see relays

[dagnabbitt]

I bought this awhile ago for my 72, haven't gotten around to installing it. My mechanic friend scoffed at the idea of using this kit - which kind of annoyed me - but then again he is colorblind and as a result doesn't show any interest in wiring. I have to admit the kit itself is covered in Chinese writing and would not inspire much confidence in myself either, had I not read about it on here.

While fiddling with it I am worried that I might have lost a component from the box. I will have to save this thread.

[MARKDTN]

You can get them on Ebay or Amazon as a generic version. It might have have cheap relays and cheap connectors. It is called an "H4 headlight relay harness" or similar. I have made my own, but it's really a pain to get all the connectors you need and good relays. I have bought cheap harnesses and upgraded the relays to Hella or Bosch as the 5 pin relays are pretty common.

There are at least 4 versions of this type harness. 1-1 relay just for both low beams, 2-2 relays (1 each low beam), 3-2 relays (1 for high beams and 1 for low beams), or 4-4 relays (2 for high beams and 2 for low beams). Variation 1 and 3 are the most popular that I have seen.

I bought one of these version 3 for my sons '97 Blazer and it made a lot of difference at night. Without changing bulbs it was a noticeable difference in light output-and it takes the load off the headlight switch.

[72SB]

FWIW the one I put in my 67 Camaro a year or so ago I got at Speedway. It was a plain wrap harness whih I assume was made here in US. This one from LMC is made in Taiwan...the connectors, wiring are done well. IDK the "quality" of relays but I suspect they are budget. Should they fail, I will replace with a known brand. Otherwise, this one works and ideally will continue to do so

For the $ you will be hard pressed to buy all the parts for $30 but if you are inclined you can roll your own

[67olds]

Out of curiosity...I have a GMC with the double headlights. Is this kit going to work for my application?
Thanks!

[mrein3]

I rolled my own "harness" and will never go back.

And yes it will work for a GMC with 4 headlights. The only difference is the "high" relay goes to one set of lights, the "low" relay to the other.

[67olds]

Originally Posted by mrein3

I rolled my own "harness" and will never go back.

And yes it will work for a GMC with 4 headlights. The only difference is the "high" relay goes to one set of lights, the "low" relay to the other.

I thought that might be the case but I hate wiring so wanted to check. Thank you!

[72SB]

Originally Posted by 67olds

Out of curiosity...I have a GMC with the double headlights. Is this kit going to work for my application?
Thanks!

if you scroll down on the link I posted, part # 36-3581 says "dual"....

and yeah the year model says these are for 73-89 1/2, 3/4 & 1 ton but the single headlight harness I got was plug & play for my 72

[MikeB]

No one has mentioned this, but in the engine compartment it's preferable to use SXL or GXL wire with cross-linked polypropylene insulation (XLPE). This insulation is tougher and has a higher temperature rating than the more common "primary" wire sold in auto parts and hardware stores, and most likely used in kits like the one mentioned by the OP.

American Autowire, Painless, and other reputable wiring harness vendors use only GXL and SXL wire depending on wire gauge.

Good explanation here: https://www.delcity.net/store/Cross!Link-Wire/p_804928

You can buy shorter lengths from Jeg's and other vendors. I used Jeg's 8-gauge SXL wire for my last truck's charging system and fuse panel feed.

Of course, the best path to brighter headlights is a quality wiring harness with 1-2 sizes larger wires than stock. In addition to much brighter headlights, you'll have brighter tail lights, turn signals, and dash lights, as well as more voltage to the ignition system. Heck, your heater fan will even blow more air, and windshield wipers will run faster!

But if a new new harness is out of the question, you can always use more relays. I'm just looking for a reason to buy something like this 4-channel solid state relay.

https://www.speedwaymotors.com/MSD-7...el,342137.html

[Already Gone]

I have one of American Autowires " Headlight Enhancement Relay Kits " for my truck and will be adding the pictured Anzo LED Headlights as well.

https://www.americanautowire.com/sho...ncer-relay-kit

[jimijam00]

Originally Posted by MikeB

the more common "primary" wire sold in auto parts and hardware stores, and most likely used in kits like the one mentioned by the OP.

There's probably a reason nobody mentioned it I suppose. Nobody I know has ever had a problem with Napa or Harbor Freight wire under the hood, ever.

[Warrens69GMC]

I bought the Toyota headlight deal for my c10, they only come with regular 9003 bulbs, but you can switch them for LED or a 9003/H4 upgrade

https://67-72chevytrucks.com/vboard/...d.php?t=828788

[kev2809]

I bought this years ago but haven't installed it yet. does it only upgrade the light output with stock wiring? I rewired my truck with an EZ wiring harness, so I'm thinking it might not be needed anymore

[72SB]

Originally Posted by kev2809

I bought this years ago but haven't installed it yet. does it only upgrade the light output with stock wiring? I rewired my truck with an EZ wiring harness, so I'm thinking it might not be needed anymore

With an old or new vehicle wiring harness, a Headlight Relay Harness is beneficial.

Headlight Relay Harness takes the full VDC load away from the light switch. The light switch then just has to trigger a relay with the voltage draw for headlights from the AUX bus near battery. All lights as a result are brighter.

If your "EZ Wiring" harness also included headlight relays than you would not need the separate relay harness

[kev2809]

Originally Posted by 72SB

With an old or new vehicle wiring harness, a Headlight Relay Harness is beneficial.

Headlight Relay Harness takes the full VDC load away from the light switch. The light switch then just has to trigger a relay with the voltage draw for headlights from the AUX bus near battery. All lights as a result are brighter.

If your "EZ Wiring" harness also included headlight relays than you would not need the separate relay harness

good point, i will to look it over. but if im remembering correctly, it did not. thanks for the info

[K10-Kansas]

Thanks for posting this 72SB. I want to solder in some relays. Does anyone have a headlight relay wiring diagram to do that?

[Accelo]

This will work.

I really liked the red solid state relay. The price is $175 on Amazon. Rated at 20a.
It would make a great looking set up.
But the do it yourself version is likely under $25 including the relays.

[K10-Kansas]

Originally Posted by Accelo

This will work.

I really liked the red solid state relay. The price is $175 on Amazon. Rated at 20a.
It would make a great looking set up.
But the do it yourself version is likely under $25 including the relays.

Thanks, this is perfect.

[Rich72C10]

I think this is one of the best mods to do for your truck, so I installed the LMC Headlight Harness very early on my truck. A little bit over a year the lights would start to flicker on after washing the truck - which I generally spray down the engine bay. It got to the point it was more than a flicker and I started to have problems days, if not a week or more after washing the truck

It seems the relays that LMC Headlight Harness uses aren't that sealed from getting moisture/water inside them. It was fairly easy to pop off the top cover and I saw moisture/water inside. LMC sent me replacement relays and I easily popped them open too but then used epoxy glue to hopefully seal them good from moisture/water getting inside. So far so good. I even bought a extra set and sealed them too, just in case.

Other than that, I love this upgrade for the headlights and dealing with the relays wasn't all that hard.

[chbracke]

I know this is sort of an old thread but has anyone used this kit from Ron Francis Wiring?

https://www.ronfrancis.com/product/96

Knowing the quality is pretty good from these guys, it seems like $70 is a decent deal.

[A1971Blazer]

Since I was installing a new harness with my LS swap, I wired the relays into a centralized load center....it controls the LS harness, fans, and headlight relays.