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Chevy 4500 headlight problem

Discussion in 'Chevy Trucks' started by ohiogreenworks, Feb 24, 2011.

  1. ohiogreenworks

    ohiogreenworks Senior Member
    Messages: 381

    Alright, let me try to explain this is a simple way. My stock headlights are very dim and when just the regular lights are on (no brights) the bright bulbs are very very dim. Sounds like a ground issue? I have no idea where to start trying to find grounds.

    What I can say is if i unplug the boss headlight harness from the original stock harness that gives the system power and I check the voltage at that point I have 11.9 volts. I then plug in the boss harness (which now makes the light work, altho very dim) that same power wire drops to 8 volts. I checked fuses, relays, etc and everything is good and all has 11.9 volts except that the boss/orginal junction in the main headlight harness.

    Any ideas?

    Truck is a 2006 4500 with boss rt3 9.2 v plow. Everything else works fine except this headlight issue. Even the plow lights work no problem:realmad:
  2. swtiih

    swtiih PlowSite.com Addict
    Messages: 1,179

    seems like the voltage should be higher then 11.9. How old is the battery and alterntor
  3. ohiogreenworks

    ohiogreenworks Senior Member
    Messages: 381

    Not real sure on either, bought the truck in october and haven't changed anything since. Truck has 46k miles on it so I assume both the batteries and alternator are original? Either way, would a bad battery or alternator only affect the stock headlights? Nothing else is wrong, everything else works great? I feel it has to be something with the stock wiring in the headlights, bad ground somewhere etc but I could be wrong..
  4. swtiih

    swtiih PlowSite.com Addict
    Messages: 1,179

    I was thinking bad ground or loose,bad or corroded connection on the supply side as well.
    Put a volt meter on the battery with the motor running and give it some throttle.
    The voltage should come up to at least 13.2v
  5. jklawn&Plow

    jklawn&Plow Senior Member
    Messages: 469

    One thing a bad ground will do is act like more resistance. As current goes up-to power lights the voltage will go down due to the voltage drops in the system. A bad ground will cause this. I think a bad battery also will cause this. A load test may show the battery has developed internal resistance and as it supplies the needed current the volatage drop is in the battery. You could check the battery voltage right at the terminals with the plow lights on.
  6. Western1

    Western1 Senior Member
    from MI.
    Messages: 752

    Those 4500's usually have the plow wiring in a bad spot for the headlights. Located on fender well where they see alot of salt spray. Might want to check all the wiring where it ties into the headlights.