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Making a wire harness

Discussion in 'Residential Snow Removal' started by mmwb, Jan 20, 2005.

  1. mmwb

    mmwb Senior Member
    from wyoming
    Messages: 114

    I am getting an older Western w/out a harness for the lights. Contact with the company indicates they no longer have one available for my ‘91 K1500. (They don’t have the frame mount either, but I know a welder that can fabricate that end.)

    When I look at the harness wiring schematics, there appears to be a relay for high beam, and a relay for low beam. I believe they are set up so that when the plow lights are plugged in they disconnect the truck lights.

    Is there a reason why I couldn’t tie the plow’s high/low hot circuits directly to the truck’s high low hot circuits, and then run the plow headlights ground and the truck headlights ground to one relay. I would use a switch on the dash to operate this relay. Switch in one position would complete the ground circuit to the truck’s head lights. In the other position, it would complete the ground circuit for the plow headlights. Seems simpler, but then why wouldn‘t the factory system be set up this way? Or is it more complex so that the plow lights connect and truck lights disconnect when the harness is connected? I’d rather not fry my harness!

    Is there a flaw in my idea?

    If so, what do you recommend?

    I will tie the parking/turn lights into the truck circuits, and will of course use quick connects and dielectric grease for all connections. Your responses will be much appreciated.
  2. SteveB(wi)

    SteveB(wi) Member
    Messages: 70

    there is no reason you cannot do that. My old Meyers is spliced right into the factory harness. No relays just an On-Off-ON DPDT switch. up plow lights, middle no lights, down truck lights. Dimmer works both. Here is a general generic wiring diagram.

    http://www.snow plowing-contractors .com/plowltwiring.html

    You'll have to take the spaces out of the link. this site musn't like the site I got it on.
  3. Ken1zk

    Ken1zk Senior Member
    Messages: 192

    I would put the relay on the hot (power) side rather than the ground side, but the dpdt switch is the easy, cost effective option.
  4. justme-

    justme- 2000 Club Member
    Messages: 2,138

    Agreed, relay the hot not the ground. Here's why: Electricity is a funny thing- it always trys to seek a ground so you may have some current finding a ground through something else (maybe a wire to the mounting bolt of the plow headlight which grounds through the plow frame to the chassis...) causing a draw- not necessarily enough to light the headlights but enough that the battery goes dead for apparently no reason. never relay or switch a ground.
    Also, Fisher's used to relay and switch the headlights the same way before the MM series. And before someone asks- no you don't want the current draw of both plow and truck lights on at the same time- the trucks wiring won't handle it.

    Oh, and you don;t need a 3 position switch, a simple dpdt 2 position is enough-why on earth would you ever need the "off" position?
  5. SteveB(wi)

    SteveB(wi) Member
    Messages: 70

    I have the DPDT because it was in stock from another project. I do use the off driving through the North woods firelanes at night to freak out the kids! I could just as easily use the headlight switch.