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Plow Headlights not working

Discussion in 'Fisher Engineering Discussion' started by DieselSlug, Nov 2, 2010.

  1. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    Hello, just hooked up the plow for the first time the other day to make sure everything checks out ok from sitting. It is a Fisher MM1 unit. When i hook the harness to the front of the truck they would automatically switch from the truck side to the plow side. Does anyone know what relay controls that, or where its located? I see two relays behind the drivers side parking light, and i replaced one of them last year. Last year i lost highbeams, so i just took a wild guess and replaced that relay and it worked. Is the other relay to switch from truck side to plow side when it makes a circuit?
     
  2. mcwlandscaping

    mcwlandscaping 2000 Club Member
    Messages: 2,557

    I'm guessing you have an SEHP system?
     
  3. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    Sorry, what does SEHP mean? The plow is run off a belt driven engine mounted pump system, with the joystick to a valve in the cab. (if that helps). Thanks!
     
  4. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,033

    Pop your connectors off and clean them up, re apply some dielectric grease. If it's still a no go, pop your covers off the headlights and check the bulb sockets, and wire connectors for corrosion. If it's still a no go then check out the guide below.

    Those two relays are for low and high beams only, if neither is working, chances are it's not those two relays.

    [​IMG]
     
  5. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    Great schematic, there is no relay for when the lights switch? Figured there would be with all the power going through it?
     
  6. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,033

    ahhh, ya know, I'm drawing a blank. This is my first time helping someone this season....I need to refresh my memory and get back to you. As far the SEHP, it stands for Solenoid Electric Hydraulic Pump. It was one of Fisher's first plow mounted pumps.

    [​IMG]
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The grill plug has a ground back through to the truck side that supplies ground to the relays when you plug in the grill connector. Thus no ground the truck lights are on, add ground, relays switch and viola..the plow lamps come on. So if they're not switching they're either not receiving ground or the 12V feed to them from the marker light wire is dead. Easy way to know that is if the markers on the plow function or not. If they don't then neither will the plow lamps.

    That's the whole purpose of the two relays in their entirety.
     
  8. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    Ill go out and check right now...
     
  9. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    Ok, went out and fired the truck. Turned on the headlights and drivers side turn signal. The side markers dont work, so the plow is totally dead. Now im going to have to put the schematic to work to find out where the issue is.