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MM2 wiring harness

Discussion in 'Fisher Engineering Discussion' started by Nummy, Sep 26, 2009.

  1. Nummy

    Nummy Junior Member
    Messages: 29

    MM2 wiring harness shorting out?

    This summer I bought a 2003 Silverado with a MM-2 fisher plow. When the plow is hooked up and the harnesses are attached the battery goes dead when the truck sits over night. Coming from the truck one of the female connectors has an 11-socket plug on it. One of the sockets on the 5-socket row, furthest from the arrow in the plug that hooks to the headlights is showing 12 volts when the truck is turned off. I feel that this isn’t right and that this is causing the truck to run the battery down. I also feel that this live 12-volt lead is the reason why the last owner said that the plow was causing a major drain on the electrical system on the truck when he was plowing. I had the alternator checked and it’s good and it had blue plow oil in it, as I just changed it this weekend so I don’t think he was having problems with ATF getting cold, turning to molasses and causing a drain on the electrical system. My question is should there be a live 12- volt wire in that harness and if not how can I correct it?
     
    Last edited: Sep 26, 2009
  2. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    hmmm, I think so. I am almost positive, but I would be very interested to know the answer as well.
     
  3. NHresident

    NHresident Senior Member
    Messages: 285

    Does it happen with the blade on/off OR both.CHK to see where the "constant pwr" red wire coming out on the veh control (cable in iso mod port 1)harness is going for pwr.Does it pwr with the key.OR is it some where else and not powering off.??
     
  4. Bruce'sEx

    Bruce'sEx Senior Member
    Messages: 873

    Everything in that plug the 11 pin one is for the lights. so when the truck is off there shouldn't be any power

    This is a quote from the a fisher mechanic's guide for straight blade, 2 plug.

    "When the snowplow is not attached to the vehicle, the signal passes through the normally closed relay contacts to the vehicle headlamps. During this time, the
    Isolation Module is inactive, placing no current draw on the vehicle's electrical
    system.

    With the snowplow attached, the Isolation Module is still inactive until either of the two following conditions are met: the vehicle parking lights are turned on or the vehicle ignition switch is turned on."

    http://www.fishersnowplows.com/pdf/27179_070001.pdf


    As for why your getting power I can't really say, it only drains when the plow is connected? wouldn't be a problem on the truck without the plow? might want the check to make sure the live wire on the control harness is tapping a power source that is not on all the time, but is only live when the key is on
     
  5. Nummy

    Nummy Junior Member
    Messages: 29

    The battery goes dead only when the harness is connected to the plow. When the key is off I still get 12-volts at the female plug. Not sure if I should have constant power with key off. I understand what you mean about (cable in iso mod port 1) but not how to check it for power.
     
  6. Nummy

    Nummy Junior Member
    Messages: 29

    I had this thought earlier today...........I wonder if the 12-volt line is live because the 2003 Silverado truck has automatic headlights that come on as needed. Causing the line to remain live. Any thoughts?
     
  7. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    I would check to make sure you have the right Module under there. Does your DRL work when the plow is hooked up?
     
  8. Nummy

    Nummy Junior Member
    Messages: 29

    Ok you got me. What is a DRL.........Otherwise everything works .Headlights, directional lights and plow.
     
  9. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    day time running lights
     
  10. Nummy

    Nummy Junior Member
    Messages: 29

    Yes , the daytime running lights work with and without the plow harness hooked up I checked that today.
    Also tried to find a short in the plow's harness and ran out of time today.
     
  11. Nummy

    Nummy Junior Member
    Messages: 29

    Thanks for the good advice ...........I'll do as suggested and be in touch.........Thanks again
     
  12. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    Hey Nummy........your in Raymond?
     
  13. Bruce'sEx

    Bruce'sEx Senior Member
    Messages: 873

    The wire I am talking about is the red power wire that will be near the plow control, most people run it to the fusebox in the cab and tap a power source. I would check to make sure thats only taping a fuse/power source thats on with the key.
     
  14. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Although there may be an error in your pin location description, if it's the pin it sounds like then it should be ground, not 12V.

    Take a look at page 6 here to be certain your pin location description is accurate. If it is indeed the correct pin then replace the under hood motor solenoid as it's back feeding 12V internally into the blk/org ground wire and thus causing a drain on the truck when the plow is connected.
     
  15. Nummy

    Nummy Junior Member
    Messages: 29

    Message to Repoman207 Yes I'm in Raymond, up on the Egypt Rd.
     
  16. Nummy

    Nummy Junior Member
    Messages: 29

    Message to B+B Thanks, yes it is socket #7 It shows that it is a ground on page 6 on the wiring diagram. I will find the under hood motor solenoid and replace it as suggested. Thanks Again...........
     
  17. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    ahhh, up on the hill.

    If ever you need a hand man, I am just around the cornor 892-3005
     
  18. Nummy

    Nummy Junior Member
    Messages: 29

    Message to Repoman207- It's good to know that I have someone near by if I get into a jam. I assume that you have a towing business. Maybe we can hook up someday. Not by accident. hahaha

    My next question for the experts is, now that I have located the motor solenoid. I'm wondering if I can get away with a old type Ford solenoid with the 2 prong set-up instead of hunting down a Fisher replacement?
     
  19. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No, they are wired differently internally. Use the correct solenoid. :nod:
     
  20. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,031

    Funny.....I use to get the dirtest looks from customers when I'ld say that. Now I don't do public. Too much of a headache and more on insurance. Straight Repos'.

    Good to see your on the right track to getting it fixed, & Welcome aboard.
     
    Last edited: Sep 27, 2009