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MMII - No power to controller after removal and reinstallation

Discussion in 'Fisher Engineering Discussion' started by retoocs555, Jan 14, 2009.

  1. retoocs555

    retoocs555 Junior Member
    Messages: 20

    I have a 2 year old MMII on a '05 superduty. I took the plow off to make a long trip and came back the next day to put it on again and now I have no power to the plow. The controller light does not light up.

    • controller switch is ON
    • I replaced both fuses
    • checked continuity on all the wires in all 3 harnesses end to end and they are all OK

    The light on the joystick should be on, even if the plow is not hooked up, but it is not lit up. When I hook the harnesses to the plow there is no change in the headlights on the truck and no action with the plow.

    This was professionally installed by a big Fisher dealer 2 winters ago. I don't beat on it, and nothing unusual happend when I took the plow off or put it back on. Since it happened after removing the plow I thought maybe the harness ends weren't making good connections, but after testing continuity could it still be that?
  2. Brian Simmons

    Brian Simmons PlowSite.com - Sponsor
    Messages: 196

    First off the control should not turn on when the plow is not hooked up. You need the red wire hooked to a switched 12 volts. When you plug the plow in you are completing the ground circuit, so I am going to guess that you have a ground issue, otherwise your lights should have swapped over to the plow. On the 11 pin light harness pin 2 is ground coming from the battery and pin 7 is the loop back to the module ( on the plow side of the 11 pin harness pin 2 and 7 are connected together in the molded plug). You can either jump pin 2 and 7 and your truck lights should shut off. If they don't, you will need to trace the ground path back to the battery to see why there is not one. Take a test light and put it on 12 volts and touch pin 2. the test light will light up if there is ground. if that side is good you will need to trace the ground from pin 7 to the module. you can also do a continuity check of pin 2 and 7 on the plow side.

  3. retoocs555

    retoocs555 Junior Member
    Messages: 20

    I have continuity on pin 2 through all the connectors and all the way back to the battery.

    But, I can't find continuity from pin 7 to anywhere on the plug for the isolation module. Do you know what wire it should be there? I think they are marked with letters.