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Lost my truck lights the other night

Discussion in 'Truck & Equipment Repair' started by Snowbully, Nov 7, 2009.

  1. Snowbully

    Snowbully Junior Member
    Messages: 7

    Hi everyone, I just picked up a used 9' uni for my 92 chevy c3500 dually dump. (Truck already has harness and mount, no controller) This truck has seen a rough life and has been hacked up pretty good by the previous "operators", (supposedly, not by the owner himself, yeah right )

    So anyway, I am getting the truck ready for work, going over the used plow and lights. After numerous corrections on the vehicle, I got all the vehicle and plow lights working, h/l beams on truck, then switching to plow lights when the 9pin is connected. It all worked fine, for about a day and a half,...

    Then last night, at the end of a hauling job, my truck headlights don't work. They act like the plow harness is connected(shutting off when the park lamps are on, turning on when the park lamps are off)). Not that it matters, but I do not have the oem headlight switch in the truck, it is 2 separate switches, so I could technically run my headlights independently without running my parking lamps, unlike factory h/l switches will not allow headlights without park lamps being on first. ( Note: It does operate perfectly fine that way as a replacement for the factory headlight switch, and it was working with the plow lights)
    So, after getting it back to the shop, I could not figure it out, and I did use the western wiring diagrams, and literature to troubleshoot.

    So I disconnected the black orange wire to the relays for now, since I need my truck lights.

    My question is, can someone explain the operation of the lights in a 2 relay setup with no DRL? In other words, when you connect and disconnect the 9pin plow connector, what happens to trigger the relays to switch from vehicle lights, to plow lights, and back? I could not seem to find a description of their operation anywhere at western's website.

    I wanna get her up and running reliably again, any help would be great.
  2. Crash935

    Crash935 2000 Club Member
    Messages: 2,377

    The relays work just like a switch, power in on one leg and back out on another when in a de energized state (i.e. truck headlights). by plugging in the 9 pin harness you complete the ground circuit which causes the relay to become energized and switch legs to the plow lights. You get the power to energize the relays from the marker light feed.
  3. Snowbully

    Snowbully Junior Member
    Messages: 7

    Thanks, I figured thats how it worked. But here is where I got confused, I know it gets the ground on black/orange when the plow is connected. Well I am getting a ground on that wire all the time and after looking at the wiring diagram, it seems that the blk/org wire is tied straight to ground at the motor relay primary lug. Other diagrams have the same black/org tied straight to the primary lug and not grounded. Which way is right or best? At least I know how to t-shoot it now.