Dim high beam on low beam

Discussion in 'Trucks [ Eighteen Wheelers ]' started by canadianredneck, Nov 22, 2015.

  1. canadianredneck

    canadianredneck Light Load Member

    Hello, I have a 95 379 Pete. I replaced the stock headlites that worked correctly with aftermarket h4 headlights. Now my high beams are on dim. Suggestions?
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  3. cnsper

    cnsper Road Train Member

    Feb 28, 2014
    You have them plugged in backwards. I am assuming you took them both out and then put the new ones in. If so, swap the plugs around. Maybe explain the issue more. When on low beam are both lights on or is the light in the wrong position on.
  4. 062

    062 Road Train Member

    Oct 20, 2013
    With regular headlights most of the time it's a weak ground,never used that type light.
  5. canadianredneck

    canadianredneck Light Load Member

    I only replaced low beams. When in the low beam position, the high beams come on dim. Can't put the bulb in backwards, its a ,3 prong. When in low beam, the high beam circuit shows 6.6v. Put the olde glass low beam in, low and high beam works perfect. Tried 2 different lites. Don't want to change Hi beams till I fix the low beam issue. Thanks
  6. Hardlyevr

    Hardlyevr Road Train Member

    Jul 30, 2009
    Some trucks for daytime running lights fed partial power to the high beams, that sounds like what you have, especially Canadian issue.
  7. kennry

    kennry Bobtail Member

    Sep 4, 2015
    Your truck a 95 shouldn't have daytime running lights.try wiggling the headlight harness inside the light bucket of the headlight assemble.mine did the same and the plug wasn't grounding right
  8. canadianredneck

    canadianredneck Light Load Member

    i ran a new ground, replaced the front harness, nothing. Put the olde glass headlights in and they work normal. I guess they need more voltage to light up as the high beam circuit still shows 6.6v. I bought another set of bulbs and put them in, still the same issue, I have no clue. Pete says drop it off and we will eventually figure it out, that scares me and my wallet.
  9. GrapeApe

    GrapeApe Road Train Member

    Jan 7, 2013
    RidinDirty11 and swaan Thank this.
  10. RidinDirty11

    RidinDirty11 Light Load Member

    Aug 20, 2015
    Grape Ape, You are correct on this. I learned this the hard way. My dad has a GMC 1500 4wd. He went to HID's. Bought the #### things from a friend he has. Worked on the #### things for about a half hour checking wiring. Swapped from one side to the other, and the problem followed. Than neither of them worked. Got really pissed now, and just threw his stock bulbs back in, and sent poor old Pop's on his way !. He gets home and calls his friend and he says hey, you need to reverse the polarity to the power box for the bulb !! So now you have factory red going to black and factory red going to black. Dad just went back out, and turned the molex backwards, and they worked perfect.

    Morale to the story. After all of these years you think I would of known better to work on electrical without a schematic and the instructions for the #### things !! Great reply.
    GrapeApe Thanks this.
  11. rank

    rank Road Train Member

    Feb 11, 2010
    50 miles north of Rochester, NY
    @GrapeApe is freaking amazing. I spent hours on this a month ago with my '86. I bet that's the problem
    GrapeApe Thanks this.
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