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Should Plow Lights & Truck Lights Be on Together?

Discussion in 'Truck & Equipment Repair' started by Steverino78, Dec 13, 2010.

  1. Steverino78

    Steverino78 Junior Member
    from SE WI
    Messages: 3

    Just bought a 10 year old Snowway plow which came with everything truckside. I put it on a 93 GMC K3500. It had been mounted on a similar series truck, but I'm suspecting that the previous truck may have had a different headlight assembly.

    My GMC has what I believe they call composite headlights where 2 bulbs are built into one rectangular headlight on each side. The initial light test showed that the low and high beams all worked fine, but I only had the lights on for a minute or so for the test. Using the plow at night, I've lost just the high beams on the truck and plow after the first 5 minutes. I'm assuming that the high current draw associated with having both the truck and plow lights on was too much. (?)

    I've previously been plowing with a tractor so this is my first truck plow. Are the truck and plow lights supposed to be on at the same time? Maybe I should switch the wiring so that the plow lights come on with the parking light segment of the stock dash light switch? (Easier said that done, I suspect.) Meanwhile, I'll be darned if I can find a fuse or relay that might have been smoked within that high beam circuit. Seems odd that there is no fuse on the fuse board for the headlights. Any help would be greatly appreciated.

  2. dave_dj1

    dave_dj1 Senior Member
    from NY
    Messages: 350

    No, all headlights should NOT be on at the same time, look under the hood for a large fuse in that fuse block. I'm not familiar with the set up you are using but I would make sure that the plow lights and truck lights are wired properly. Is there a switch that is supposed to toggle between the two?
  3. Steverino78

    Steverino78 Junior Member
    from SE WI
    Messages: 3

    No there is no switch that came with the harness. I may have to find a schematic from Snowway for this harness. And I've scanned the Chilton schematic for a fuse, relay or fusible link and have not been able to find that either. Now knowing that the two should not be on at the same time does help me already. Next step is to find the fuse as there has to be one somewhere. There is a Potter & Brumfield relay that came with the Snowway light harness that may be suspect too.
  4. bill7101

    bill7101 Member
    Messages: 34

    theres a fuse for the headlights in the panel by your left knee, yes having both sets of headlights on is way too much draw for the setup, it should have a switch to control between plow lights and truck lights i put it through relays when i installed mine on a 92 GMC2500 instead of running hot wires all over the place to the toggle switch
  5. Steverino78

    Steverino78 Junior Member
    from SE WI
    Messages: 3

    The main fuse board by my left knee, as you stated was the first place I went and found it odd to not find any fuse identified as headlights. I pulled each fuse regardless, just to check for one that was blown and nothing. This is a diesel truck but I can't picture why that would make the headlight circuitry any different. I've got an older 88 Chev sitting here so I'll go look see if that has headlight fuses on that main board. Little by little this is unfolding. You mentioned you put a relay in to avoid running the hot leads all over so I now suspect that the relay that came with the harness might be for that very purpose and it might be faulty. They're relatively cheap to replace to I'll get one and swap it out to see if that cures all the problems. (But that still leaves me hanging in regards to where the stock headlight fuse is!)
  6. hitachiman 200

    hitachiman 200 Senior Member
    Messages: 262

    there should be another fuse box under the hood,try there. when you plug in your harness to the plow it grounds the relay which shunts the power to your plow lights. this relay is energized when ever the plow is plugged in. I generally replace this at the start of each season and always carry a spare along with a spare pump motor soliniod

    Good luck this season