03 GMC ultra mount 3 port iso headlight issues

Discussion in 'Chevy Trucks' started by guinelle1, May 20, 2020.

  1. guinelle1

    guinelle1 Junior Member
    Messages: 6

    have 03 gmc 2500 with western ultra mount. has 3 port iso module. plow has been on this truck only and was installed by a dealer.

    truck headlights operate as normal. plow running/turn signals work as normal. first driver side low beam was not working. no power. checked wires to the iso and nothing coming from the iso. while was messing with it iso started clicking rapidly and would all the lights off. still no driver low beam, now i have no pass high beam. what is the best way to test the iso? been reading threads everyone says these dont fail. also all other threads mention people swapping between trucks. not the case here.
     
  2. cwren2472

    cwren2472 PlowSite Fanatic
    Messages: 8,324

    New install or this stuff has been installed for a long time?

    Is this on the truck, on the plow, or both?

    Which harness specifically did you "mess with"? The A harness going out to the plow or the B/C harness going to the truck lights?

    Use a test light or multimeter to verify all functions coming in and out or take it to a dealer who can plug it into a test unit to verify it's working correctly. But if you "messed with it" and it started clicking, it is very unlikely that the issue has anything to do with the circuits inside.
     
    Last edited: May 20, 2020
    m_ice likes this.
  3. OP
    OP
    guinelle1

    guinelle1 Junior Member
    Messages: 6

    sorry i was in a hurry making the post, by "mess with it" i checked continuity on output wire to the plow side low beam and it was ok, nor shorted to ground. i was not sure if this truck uses postitive common? but i dont think so. for 170 we ordered the module.

    this plow has been on this truck about 6? years. as already stated ALL truck side lights work fine. when plugged into plow i have no driver side lowbeam, and now most recently now passenger side high beam. everything else works.

    also i was not doing anything when the module did its little freak out, i plugged it all back in and turned the lights on. i was standing next to the truck looking at the wire diagram and heard 4 or 5 loud rapid clicks. very obviously from the module, then all the lights running and headlights shut off. i went in the truck turned the switch off and back on and they came back on but still no driver side low, also lost passenger high beam after that.
     
  4. cwren2472

    cwren2472 PlowSite Fanatic
    Messages: 8,324

    The module isn't going to fix it. It's almost certainly the 11 pin harness going to port A. That truck should be a 26357
     
    Philbilly2 and Western1 like this.
  5. Western1

    Western1 PlowSite.com Addict
    from MI.
    Messages: 1,889

    How long ago did everything work correctly? Assuming it did at some point? Was a headlight bulb changed?
     
  6. Western1

    Western1 PlowSite.com Addict
    from MI.
    Messages: 1,889

    Like “c” said. Very rarely the module. I would bet the 11 pin as well.
     
  7. OP
    OP
    guinelle1

    guinelle1 Junior Member
    Messages: 6

    Which wire off the 11 pin? The module was supposed to get here tonight. The output wire to the low beam is good. The inputs should be good since the truck side works fine. Not sure what else needs to be checked. This is fairly simple. Take factory lights into the module and it’s not coming out.

    this was installed by a dealer approx 8-10 years ago.

    we are looking to sell the truck w/ plow but it would be nice if the lights worked before we sold it.
     
  8. OP
    OP
    guinelle1

    guinelle1 Junior Member
    Messages: 6

    Also headlight bulbs were fine. Tested them and work fine.
     
  9. cwren2472

    cwren2472 PlowSite Fanatic
    Messages: 8,324

    Sounds like you got the module all diagnosed then. Good luck!
     
  10. Western1

    Western1 PlowSite.com Addict
    from MI.
    Messages: 1,889

    Let us know! Good luck
     
  11. OP
    OP
    guinelle1

    guinelle1 Junior Member
    Messages: 6

    Well you guys were right it wasnt the module. but assuming the inputs were good was a mistake. i think last year either me or the mechanic changed the headlight bulb on the truck side. and i didnt notice the plug can be flipped if you have positive common. so the driver side bulb was some how still working. but not feeding the module to output power to the plow lights. flipping the plug fixed it.
     
  12. Western1

    Western1 PlowSite.com Addict
    from MI.
    Messages: 1,889

    Glad you figured it out. That’s more common when hooking it up. Easy to not realize it can be flipped. Good luck!