headlight problems

Discussion in 'Peterbilt Forum' started by coulds, Apr 1, 2013.

  1. coulds

    coulds Bobtail Member

    24
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    Nov 4, 2012
    Richmond,Va
    0
    I have a 94 379 pete when I turn on the low beams you can see the hi beams on a little. When I disconnect the hi beams the lo beams get brighter do anyone have any idea what the problem could be??
     
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  3. eeb

    eeb Heavy Load Member

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    Mar 24, 2013
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    Weak ground
     
    coulds Thanks this.
  4. coulds

    coulds Bobtail Member

    24
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    Nov 4, 2012
    Richmond,Va
    0
    Ok thanks eeb where would I start to look for the weak ground
     
  5. DGStrong71

    DGStrong71 Road Train Member

    1,279
    407
    Feb 22, 2013
    70° west
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    Resitor value changes somewhere in the circuit. Normaly they fail open but they can and do change value. I have a prostar that continually burns up the wiring for the left headlight. I have to unplug them during the day when they are not needed to prolong the life of the wiring for a couple more months until I get a new truck.
     
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  6. carrkool

    carrkool Heavy Load Member

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    494
    May 10, 2012
    adah, pa
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    look at the plug... both my classic did the same thing you have going on. needed new plugs. the ground on the plug was week and it was looking for a ground in the system so it would turn on the highbeam slightly.....we just went ahead and ran all new wire and plugs since we had to do the plugs....
     
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  7. coulds

    coulds Bobtail Member

    24
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    Nov 4, 2012
    Richmond,Va
    0
    Carrkool If I ordered a new wiring harness would that fix the problem I did put new plugs on all four lights but still have same problem??
     
  8. carrkool

    carrkool Heavy Load Member

    883
    494
    May 10, 2012
    adah, pa
    0
    Ok this is on a 379. Common area on them if its not the plug on the lights is just inside the hoos where the wiring come out of headlight bucket. it bends down right there and goes down to the bumper area which is the 3 place to look. before i bought a new harness i would check these areas and the factory plugs there. they tend to break in these spots.

    Personal if you find that it is in one of these spots i would buy about 10 feet of heavy duty 3 wire rubber coated wire and get rid of all the factory plugs. you could even get the 4 wire share the ground and run your turn signal through it also. better wire no more plugs to break and one connection point.....
     
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  9. OldHasBeen

    OldHasBeen Road Train Member

    1,269
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    Dec 16, 2010
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    Once several years back driving a 76 or 77 conventional KW my front right headlight had a bad ground & on dim would not be on at times. While at a cooler north of LA I opened the hood & worked it over replaing the ground wire. Thought I had it fixed. But coming back east I got pulled over on I-10 going thought Van Horn, TX.

    I did not realize the headlight had gone out, & when the state trooper stopped me I said, "Surely I wasn't speeding?" he said, "No, you've got a headlight out."

    We walked to the front of my truck & sure enough it was not on. Without a thought I reached out & bumped the fender with my hand & it came on shinning brightly, & I said, "Looks like its burning now."

    He them said, "Oh, your one of those smartXXXXX truck drivers, now I'm going to give you a ticket instead of a warning."

    I quickly apologized to him letting him know I did not mean it that way & about having just worked on it thinking I had it fixed. He accepted it & only gave me a warning ticket.

    Strange, after that that headlight never gave me another moments problem. :biggrin_25520:
     
  10. eeb

    eeb Heavy Load Member

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    Mar 24, 2013
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    Follow the wire, checking for damage and check connectors and terminals for corrosion or damage. I've seen many corroded terminals bypassed and damaged wires repaired with heat shrunk butt connectors, helluva lot cheaper than a harness. As you know, electrical problems can be a major pain to diagnose and repair, just have to dig in.
     
    coulds Thanks this.
  11. Carpenter Trucking

    Carpenter Trucking Bobtail Member

    3
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    Mar 30, 2012
    lawton , ok
    0
    I got a headlight issue also. 92 pete 379 low beams work fine, when I turn on the high beams all power on the right side dies out, now low or high beams? the left side works just fine.. I have replaced the switch, relay, wires where they were cracked inside the head light asembly , I have no idea where to look next. I have even ran a jumper wire from the left the right and pops relay? no idea where to look next any help would be greatly appricated
     
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