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mm2 trouble w/headlights,help

Discussion in 'Fisher Engineering Discussion' started by massbowtie, Jan 1, 2006.

  1. massbowtie

    massbowtie Member
    Messages: 97

    im trying to figure out what is wrong with the lights.im working on an 02 gmc 2500hd,with a mm2 3 plug,11 pin for lighting.i beleive this to be an earlier mm2 as it doesnt have the one handle pin instead it has the 2 you have to release individually. it also has the instact pump.anyway the problem is when you hook up the plugs it switches over to plow lights but on low beam the truck headlights stay on.when you switch to high beam the truck lights go off and hi beam works on the plow.im thinking its the truck headlight switch.it has the auto lights but has the over ride button but it doesnt work and the truck has no daytime running lights either.any ideas would be greatly apreciated.thanks.
     
    Last edited: Jan 1, 2006
  2. Mick

    Mick PlowSite.com Veteran
    from Maine
    Messages: 5,546

    First thing, check your plug to the plow. Are any pins loose or bent? Is there any corrosion? Is the plug seating completely? Look into the female plug. Is there any corrosion? Wiggle the plug when it's connected to see if the truck lights go out.
     
  3. Crash935

    Crash935 2000 Club Member
    Messages: 2,377

    I doubt that its the headlight switch. Heres how the lights work, by plugging in the connector at the grill you complete a ground circuit going back to the isolation module. The completed ground causes the I.M. to switch where power for the lights goes (truck or plow). Since you have low beams and high beams the switch in the truck must be working. Theres the possiblity that because the DRL's are not working (check fuses on truck and DRL bulbs) that its causing the truck to send a false signal or that the IM is not getting a signal from the DRL circuit, or that the IM has gone bad. I would start with the problem of the DRLS.
     
  4. massbowtie

    massbowtie Member
    Messages: 97

    thanks

    mick,
    i doubt its the plugs.there brand new,long story short the plug was cut off of the truck and the 11 pin is the only one fisher doesnt make a repair plug for so you have to buy complete harness to repair that plug so thats all new.

    crash,
    what is it your referring to when you say (IM)? the fuse is good for drl but i didnt check the bulbs.ill check into that.
    as for why i was thinking the headlight switch is bad is because the over ride wont work so im still thinking the truck headlight switch has a problem.
    i probably wont work on the truck until wed as were getting more snow.thanks again for the help.ill post back what i find
     
  5. Crash935

    Crash935 2000 Club Member
    Messages: 2,377

    Just out of couriosity, check the pink wire coming into the isolation module at port 3 for power, this is the drl feed coming into the iso mod.
     
  6. rtm038

    rtm038 Senior Member
    from NJ
    Messages: 231

    Did this plow come with your truck? If so, did it work properly last year? If the plow did not come with the truck, in addition to checking the pink wire, call your local dealer and run the Isolation Module (a.k.a. "IM") part number by them. If memory serves me some GM trucks with the DRLs (a.k.a. Daytime Running Lights) required a special IM.
     
  7. Merc1100sc

    Merc1100sc Senior Member
    Messages: 245

    we just had the same prob on my buds 03 gmc. the connectors behind the trucks headlights were backwards. the gray and black ones i mean. pull one of the headlights out of the truck and check these. i didnt think they would let you plug into the wrong connection on the truck, but, it did.
     
  8. massbowtie

    massbowtie Member
    Messages: 97

    ill know more tomorrow

    havent been able to work on it with the weather and my schedule,ill be working on it again tomorrow.ill wirte the tips down and check it all out and reply.


    crash,
    ill check that pink wire,im assuming thats the feed to the plow lights to energize the drl circuit ?

    rtm,
    its not my truck.the history i shady at best.something caused a fire last year and the 11 pin light plug got melted.somebody used a regular twelve pin plug for a temp repair to finish the season.thw owner said it did not do this before the melt down.anyway i replaced the 11 pin plug from the module right to the headlights as its the only way to repair an 11 pin plug.i checked the drl fuse.the ebrake appears to be off.i was leaning toward the switch or like somebody else said maybe the drl bulbs are bad and thats causing it. i dunno

    merc,
    ill check it out tomorrow.that sounds plausible.anyway the owner doesnt care the drls dont work,hes more worried about the extra drain on the battery with the additonal lights running.

    :salute: gentlemen thanks again for the feedback,this is why i like this site,very informative.i was at a loss but now i have more ammo to try to figure it out.ill post my results once i check all these things posted.
     
  9. Merc1100sc

    Merc1100sc Senior Member
    Messages: 245

    Im just rereading this again. Whoever rewired it temporarily after the fire, did they do it right. Could have shorted out the IM if not right. I would think the fuses would protect it, but, never know.
    Also, this is a 2002 and has the override control for the DRL's. I thought to the only way to **** the DRL's off on Pre-2003's was to quickly press the dome-light override button in 4 times.. i thought 2003 was the first you of the new highlight selector switch with the auto feature.
    also, are you sure you wired that new harness correctly. not implying anything negative here, but, never hurts to double check. i know we all make the smallest mistakes.

    if i were you, i would start from square one. if all the plow functions work fine, then, you know the plow control harness is ok. second, unplug all the light connections that arent factory and make sure the truck itself is fine, then hook everything as you would a new install. have you tried hooking up to another mm2 to make sure everything plow-side is ok also?
     
  10. massbowtie

    massbowtie Member
    Messages: 97

    what i know

    Im just rereading this again. Whoever rewired it temporarily after the fire, did they do it right. Could have shorted out the IM if not right. I would think the fuses would protect it, but, never know.
    Also, this is a 2002 and has the override control for the DRL's. I thought to the only way to **** the DRL's off on Pre-2003's was to quickly press the dome-light override button in 4 times.. i thought 2003 was the first you of the new highlight selector switch with the auto feature.
    also, are you sure you wired that new harness correctly. not implying anything negative here, but, never hurts to double check. i know we all make the smallest mistakes.

    if i were you, i would start from square one. if all the plow functions work fine, then, you know the plow control harness is ok. second, unplug all the light connections that arent factory and make sure the truck itself is fine, then hook everything as you would a new install. have you tried hooking up to another mm2 to make sure everything plow-side is ok also?

    merc,
    as for the rewire,everything was working other than the low beam truck lights staying on with the plow plugged in,and they go out when you flip it to high beam and all works on the plow lights,before and after i replaced the harness.as for the drls yes this truck does have the manual overirde by pushing the dome light button,it is an 02.the over ride doesnt work which is why i was thinking truck headlight switch.the drls dont work but i didnt check the bulbs yet but the fuse was good for the drl`s.
    as for the new wire harness install,the 11 pin is the only one that you cant buy repair plugs for.i had to run a new harness from the module(plug in) out to the head lights,literally right to the bulbs is all new on the plow.all my wiring in the head lights was one wire for one wire at a time.
    everything works on the plow,up,left down right, directionals etc.i havent tried another mm2 which is another option available after i try a few other things like you just said to disconnect aftermarket and check the original.im going to figure it out i just cant work on it between storms.worked on it saturday and it went out for snow early am sunday and again today.just havent had time to get back to it yet
    thanks
     
  11. Merc1100sc

    Merc1100sc Senior Member
    Messages: 245

    gotcha... well good luck.. i hope you get it figured out..
     
  12. Crash935

    Crash935 2000 Club Member
    Messages: 2,377

    I'm with Merc, go back to the original and see what happens.

    You have to get that thing fixed though, couriosity is killing me...