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Headlight Issue on Unimount

Discussion in 'Western Plows Discussion' started by Stan, Nov 15, 2010.

  1. Stan

    Stan Senior Member
    Messages: 579

    Bought a 1994 Chevy 3500 several months ago and came with a Western. While driving home one night (plow not on truck) the headlights went out for no apparent reason. I disconnected the Western harness and utilized the factory connections which worked. Ordered 2 new relays and crimped new ends on all wires, old terminals looked questionable. Hook everything up including the plow, no headlights. Downloaded the Western troubleshoot guide and here's where I'm stumped:

    No voltage at terminal 87A
    with red (high beam) or orange
    (low beam) wires

    Disconnected black/orange wire from terminal
    85 of both relays and had 12V at terminal 87A

    Black/orange wire in vehicle
    harness is shorted to ground.
    Repair wire.....I traced these wires from left to right side of vehicle and found absolutely no problems of the sort.

    Can anyone help?
     
  2. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    How many realys are in the wiring harness on your truck?
     
  3. hightop

    hightop Member
    Messages: 47

    The black/orange wire is the ground which activates the relay and switches power from 87a (truck headlights) to 87 (plow headlights) The black/orange wire grounds when the harness (9 or 12 pin) is plugged into the plow harness. The relay is normally connected from terminal 30 to 87a when it's de-energized.

    Since you have voltage @ 87a when you disconnect the black/orange wire, you must have a short to ground you missed.
     
  4. Stan

    Stan Senior Member
    Messages: 579

    Just 2 behind left headlight
     
  5. Stan

    Stan Senior Member
    Messages: 579

    According to the schematic, the blk/orange wire is routed to motor relay near battery. The only relays I have found are the high and low. Would it be possible to have a problem with that relay if I can find it?
     
  6. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    No that is the ground that is coming from the motor relay (aka solinoid). The or/blk is what grounds the solinoid so it can close.
     
  7. hightop

    hightop Member
    Messages: 47

    What philbilly said is correct. The black/orange coming from your 2 relays shouldn't be grounded until the plow harness is plugged in, when it ties into the plow headlight ground & activates the relay, which switches from 87a to 87, turning off your vehicle headlights & turning on the plow headlights.
     
  8. Stan

    Stan Senior Member
    Messages: 579

    Sorry for my ignorance but now I understand how it works. So in theory the plow lights should be on. If I was to disconnect the blk/org wire from the solenoid it should break the circuit to operate vehicle headlights?
     
  9. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    Ok, here is my guess.

    Without the plow on, but having the low beam headlights on,
    You should see 12v on position #30 (yellow wire on low beam relay), then 12v on #87A (Orange on same relay)

    If you do not see 12v on the yellow wire, you problem is some where in the harness between the relay and and the plug that comes from the truckside of the headlight harness. If you have 12v there but not at 87A, then your relay is no good. Pull the yellow and the orange wires off of the relay and put a jumper in there. This will verify that that is the problem.
     
  10. Stan

    Stan Senior Member
    Messages: 579

    In the shop now and pulled this thread up for referance. I traced or/bl wire as per scematic grounding @ self taping screw that holds in solenoid. I traced this wire carefully back thru into the relay. Several inches up from relay I cut the wire and had headlights. Re-spliced and no headlights. Disconnected or/bk from solenoid and have headlights. Went to the 12 pin connector and applied ground with the power probe to pin #5, which turned headlights off. Scratching my head of eiher running the or/bk wire to a toggle switched to ground OR go home and have a beer. Think I'll grab the beer. BTW, both relays are brand new.
     
  11. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    Call me crazy but do you have the 87A and 87 switched. It sounds like when ever you hook up your plow it turns on your truck lights.
     
  12. Stan

    Stan Senior Member
    Messages: 579

    I had the front grill off and inspected the harness. I cut back some of the factory wire loom and do not see any issues. The above post was with the plow off. What throws me off is the or/bl wire that grounds @ solenoid is an absolute ground to the headlight relays. Without that wire attached it solves the problem. I don't think it has anything to do with the plow side of the harness because the problem started by just driving down the road without it on.
    Just a shot in the dark, could the cab controller be at fault?
    By looking at the schematic (plow not connected it appears the brn wire to the park lamp which leeds to the plow connection activates the ground circuit when plow is connected? If not what does?
     
  13. Stan

    Stan Senior Member
    Messages: 579

    Not switched
    orn to 87a, blk to 87
     
  14. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    The only way that the relay should ever be energized is if the plow is hooked up and the parking lights are on. The ground on 85 goes out through the grill connector and gets hooked through the S1 S2 and S3 solinoids then hooks to the motor and goes back to the battery via the 2 plug conector in the grill.
     
  15. Stan

    Stan Senior Member
    Messages: 579

    So with that said this points out to be a faulty connection somewhere to the plow connection...right?
     
  16. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    Are you sure that 87A and 87 are in the same spots on these relays as the last ones? If you disconect the ground, it de energizes the realy switching the 12v from the headlights over the the N/C side of the relay. Mayber these realys are different and we need to be talking in terms of N/O and N/C?
     
  17. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    Not sure yet, I am still thinking it is back at the realys. Your headlights should be on with no plow connected.
     
  18. Stan

    Stan Senior Member
    Messages: 579

    Would park lamp sockets feed back a ground?
     
  19. Philbilly2

    Philbilly2 2000 Club Member
    Messages: 2,633

    I don't understand the question. Could you rephrase for me?
     
  20. Stan

    Stan Senior Member
    Messages: 579

    If there was corrosion in the truck parking lamp sockets or a bad bulb would that feed an unwanted ground signal back to the relay?