Headlight Harness Problems!
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Senior User
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Headlight Harness Problems!
Just purchased my Heavy Duty headlight harness from LMC and installed it today.My problem is that my headlights stay on all the time regardless of the switch. Is this the sign of a bad ground,bad relay,or something else?
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Senior User
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That was my first thought,the only problem I had with the harness was that the relays looked cheap.......so,rather than call LMC and have them send more crap relays,is there any way to adapt their relay connector like this-
to one like this
Without cutting off and splicing in the new connector?
to one like this
Without cutting off and splicing in the new connector?
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
Kind of. Both harnesses use female quick connects, these have little tabs between the retainers that are pushed out and lock them in place. If you take a small awl or pick and push this tab flush, the connector will slide out. With all of the connectors loose, you can do the same with the bosch relay base.
The relay that was provided was SPST, and the replacement base is SPDT. You will not put any wires in the 87a spot.
The relay that was provided was SPST, and the replacement base is SPDT. You will not put any wires in the 87a spot.
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
If you don't have the relay already, you don't have to buy the base. The spade terminals will work just fine without it, you will need to insulate them. The relays are probably cheaper at stores like radio shack. Pick up some heat shrink while your there to cover the terminals.
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Senior User
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Figured I'd switch the bases just for convenience, think they have a relay wiring kit with two 40a relays and the pigtails for a few bucks,if all goes well hopefully that'll take care of my problem.....
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Post Fiend
Joined: May 2006
Posts: 10,007
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From: Central Florida
If you find them dirt cheap locally, I'd love to know where. Relays are $8-12 and bases are $4 easy if you can find them. Online the relays are $2-5 each, I haven't checked the bases.
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Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
I know how the bosch goes.
85 goes to ground. 86 is the positive switched power (your switch). 30 is what your controlling in this case your lights. 87 is the power input for the lights.
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..| The two vertical on top are 85 and 86. The vertical on bottom is 30. The middle is 87a and the top horizontal is 87.
I would suspect one half your old harness is the coil (85&86), the other half is 87 and 30.
85 goes to ground. 86 is the positive switched power (your switch). 30 is what your controlling in this case your lights. 87 is the power input for the lights.
|=|
..| The two vertical on top are 85 and 86. The vertical on bottom is 30. The middle is 87a and the top horizontal is 87.
I would suspect one half your old harness is the coil (85&86), the other half is 87 and 30.
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I've got both the power terminal and light terminals figured out,the wires that plug into my existing harness has me stumped though 
Have a brown,white,and a blue/white that splits to both relays. I'm thinking the blue/white goes to the switched source,and the brown and white are the grounds for each relay?...
Have a brown,white,and a blue/white that splits to both relays. I'm thinking the blue/white goes to the switched source,and the brown and white are the grounds for each relay?...
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
I can't go by the wire colors. It's time to break out your DMM. With the relay disconnected, only one wire should have power, this is your battery source. With the relay still out and the switch on, there should be two wires with power, the new one is your switch. Switch your DMM over to continuity or ohms, and put one probe on the power side of the lamp harness, the wire that has continuity to both harnesses will be the output. The remaining one is the relay's ground. Actually it doesn't matter. As long as you don't use a spike suppression diode relay. The current to the coil can go in either direction.