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Ford / MM1 / no driver side head light or plow lights

Discussion in 'Fisher Engineering Discussion' started by chachi, Nov 4, 2011.

  1. chachi

    chachi Junior Member
    from NY
    Messages: 16

    Hi everyone -

    I read about a million posts about what I'm about to write about. I have found some really great info and have tried most of the things I've found here.

    I have a 98 F250 (light duty). I got the truck with all of the truck side parts (harness, push plates, controller, iso, etc.). The truck as three plugs on the truck side. I did not get a plow with it though.

    I found a plow set-up used on craigslist. When I went to put it on the truck I found that the plow had only 2 plugs.

    After searching my friend "google" it led me to this site and a bunch of posts pertaining to exactly that same issue. Thanks to the advise from all of you, I was able to order the 2 needed harnesses (26359 and 26347).

    We installed both harnesses, attached the plugs to the truck and the plow worked perfect!!

    So while the plow now works great (up, down, and right / left), but no plow lights. While trouble shooting the plow lights, we found we are NOT getting power to the harness from the ISO module. To make matters worse, with the plow completely off, the driver side low beam doesn't come on with the switch. The passenger side low beam works fine and so do both side's high beams.

    If we test light the wires into the driver side, we find no power on the low beam side wire. The wire is Orange. We found another Orange wire at the ISO module (port 3) and put 12 volts to that wire. When we do that, the driver side light comes on right away. Reading some of your posts here led me to the 3 wire connector near the ISO (with the jumper). I jumped it both ways with a screw driver (never outside pin to outside pin), all with the lights on. Neither jumped selection would work.

    I then took both lights out and took the harness out of the loop and hooked just the original truck wiring plugs into each head lamp.... Same problem - still only the passenger side low beam and both high beams work.

    My first thought is put switched 12V power the Orange wire found at the ISO that powered the driver side low beam. My second thought is to wire the driver side low beam wire, with the passenger side low beam wire..

    Any additional thoughts?

    Thanks in advance,

  2. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,039

    It's obviously a truck issue, not a plow wiring issue. Don't complicate matters by rigging the plow wiring to suffice a real solution to the issue.

    If it were me, I would remove the plow connections as you have, and plug the factory connectors directly into the headlamps. I would then check that headlight bulb, even replace it for good measure. Then track the wiring with a test light, starting with BOTH sides of the factory headlamp connector, all the way back into the truck, or until you find the issue. Chances are it's either a bad factory connector, or a compromised wire in the near vicinity. Otherwise take it to your auto shop to have it done.

    Again, don't bother complicating the issue with plow wiring, stick to the ultimate problem. It's worth it to do it the right way, especially in this scenario.
  3. chachi

    chachi Junior Member
    from NY
    Messages: 16

    Agreed RepoMan.

    The bulb was replaced earlier for good measure (great minds think a like) and confirme to work. I will continue troubleshooting tomorrow.

    I def will get the truck's lights to work before I go further with the plow wiring.

    While we attempted to wire the plow lights last week, we couldn't get even signals or parking lights to work either. I think I've inadvertenly already repaired this while troubleshooting the head light issue. Found a 15amp fuse blown in the wiring from the plow harness near the ISO mod - my guess now is that it had been for the signals / parking lights.

    thanks again,