LMC Heavy Duty harness (quad headlight )

Godwinaustin

Junior Member
Joined
Apr 8, 2020
Posts
21
Reaction score
3
Location
Wyoming
First Name
Jon
Truck Year
1983
Truck Model
K20
Engine Size
350
Just purchased this from LMC for my 83 K20 with the quad headlights.
I connected the male plug on the LMC harness to the female passenger side low beam plug for the factory harness. Connected everything else.

low beams work normally

High beams work but in addition the driver side low beam is on as well (so I have 3 lit headlights) Any ideas what’s going on ?
 

Customblue

Full Access Member
Joined
Feb 28, 2018
Posts
201
Reaction score
196
Location
Locust Grove, Va
First Name
Brandon
Truck Year
1986
Truck Model
K10
Engine Size
489
Did you connect them to the first plugs closest to the bulkhead? You should be able to abandon the wires after the headlight plug(s) on the drivers side.
 

Godwinaustin

Junior Member
Joined
Apr 8, 2020
Posts
21
Reaction score
3
Location
Wyoming
First Name
Jon
Truck Year
1983
Truck Model
K20
Engine Size
350
Did you connect them to the first plugs closest to the bulkhead? You should be able to abandon the wires after the headlight plug(s) on the drivers side.

What do you mean the first plugs closest to the bulkhead ?

there is only one male connector from the LMC Harness , it has three prongs and I plugged that into the factory passenger side headlight Harness.
 

Craig 85

Full Access Member
Joined
Jan 25, 2017
Posts
3,578
Reaction score
3,380
Location
Nashville, TN
First Name
Craig
Truck Year
1985
Truck Model
K30 SRW
Engine Size
454/TH-400/NP205
If you have a 4 headlight system, all 4 lights should be on Hi-beams. The high beam part of your low beam bulb could be burned out.
 

Godwinaustin

Junior Member
Joined
Apr 8, 2020
Posts
21
Reaction score
3
Location
Wyoming
First Name
Jon
Truck Year
1983
Truck Model
K20
Engine Size
350
If you have a 4 headlight system, all 4 lights should be on Hi-beams. The high beam part of your low beam bulb could be burned out.

that’s helpful ... I wasn’t sure if all 4 should be on with high beams on.... so the low beam lights (top row) are dual filament then ?
 

Bennyt

Full Access Member
Joined
May 17, 2019
Posts
427
Reaction score
504
Location
Surprise
First Name
Ben
Truck Year
1977
Truck Model
C10
Engine Size
350
I tried the LMC harness on my '06 Suburban a few years ago as it was supposed to make my lights brighter and I would notice from new the bulbs would dim a bit every time something else was turned on.. While I may have noticed a very marginal increase in light output; my bulbs would burn out at about every 3-4 months and when one burned out the other would go dim to where I had almost no light at all. I gave up and removed the harness and installed LEDs made specifically for the application. I ended up with no dimming and much brighter lights. The LMC harness looked and felt cheap and I considered trying the harness from Painless Wiring but got what I was looking for with the LED's.
 

Craig 85

Full Access Member
Joined
Jan 25, 2017
Posts
3,578
Reaction score
3,380
Location
Nashville, TN
First Name
Craig
Truck Year
1985
Truck Model
K30 SRW
Engine Size
454/TH-400/NP205
that’s helpful ... I wasn’t sure if all 4 should be on with high beams on.... so the low beam lights (top row) are dual filament then ?

Yes
 

Juan Cano

Full Access Member
Joined
Jun 7, 2021
Posts
86
Reaction score
34
Location
Warwick, RI
First Name
Juan
Truck Year
1986
Truck Model
C10
Engine Size
350 Goodwrench Crate
What do you mean the first plugs closest to the bulkhead ?

there is only one male connector from the LMC Harness , it has three prongs and I plugged that into the factory passenger side headlight Harness.
Hi; this is an old post but, working on doing this on my 1986 C10. So the 3-prong plug, you put that on the upper light connector that is on the wiring harness? Then the rest of the plugs just go to the light? Confused about this.
 

Craig 85

Full Access Member
Joined
Jan 25, 2017
Posts
3,578
Reaction score
3,380
Location
Nashville, TN
First Name
Craig
Truck Year
1985
Truck Model
K30 SRW
Engine Size
454/TH-400/NP205
Hi; this is an old post but, working on doing this on my 1986 C10. So the 3-prong plug, you put that on the upper light connector that is on the wiring harness? Then the rest of the plugs just go to the light? Confused about this.
Yes the harness just plugs into the to the three prong plug. Either side should work. Are you keeping stock style bulbs? I'm running H4/H1 bulbs which caused me to have to re-pin the plugs.
 

Juan Cano

Full Access Member
Joined
Jun 7, 2021
Posts
86
Reaction score
34
Location
Warwick, RI
First Name
Juan
Truck Year
1986
Truck Model
C10
Engine Size
350 Goodwrench Crate
Yes the harness just plugs into the to the three prong plug. Either side should work. Are you keeping stock style bulbs? I'm running H4/H1 bulbs which caused me to have to re-pin the plugs.
I figured it out!! Thank you. I didn't change the bulbs. Someone said to just buy nicer quality headlights. But maybe next year. Don't drive at night that much.
 

Camar068

Supporting Member
Supporting Member
Joined
Feb 5, 2014
Posts
3,182
Reaction score
1,454
Location
Kentucky
First Name
David
Truck Year
1986
Truck Model
K10/LM7 5.3/4L60e/np208/3.73/32"
Engine Size
10 yrs Air Force
installed harness today. Below is before and after numbers I took about 6" from the bulb. This is the highest/steady number I cold get on each. Yes I've a light meter. Need to replace the passenger side Hi beam (lower bulb). These are Sylvania Xtravision bulbs.

full
 

Forum statistics

Threads
35,557
Posts
748,098
Members
24,482
Latest member
JohnC
Top