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  1. #1

    Default Dim headlight after fog light install

    My truck didn't come with fog lights but I was given a pair of aftermarket ones years ago so I thought I would throw them on the truck. The idea was I would use relays so they they would come on when the headlights are on and I don't need to run a seperate switch. I used standard 4 post relays and I tapped into the orange wire on each headlight connector for my reference wire. I ran new wires with inline fuses off the terminal in the red battery box and ran the wires in their own looms so they were out of the way. The fog lights are grounded to the frame and the relays are grounded to the steel beam under the front of the hood. At first, everything worked good. Then the fog light started working intermitently, then the driver's one didn't work at all. The passenger one worked sporadically, and now the passenger headlight is always dim (high or low) when it comes on. It puts out barely enough light to see that it is lit.

    I tried replacing the bulb, that didn't fix it. I've removed my wiring from the headlight wiring in case that was interferring somehow and it still doesn't work right. The way these headlights get their power confuses me because it seems like the headlights are always getting 12 volts of power and I don't understand what is differentiating between low and high beam. Does anyone have an idea what might be wrong?
    2000 Silerado Extended Cab - 4.8L V8 - 4L60E - 4x4 - Bone Stock - 189K - Considering upgrades

  2. #2
    Master Mechanic clgoch187's Avatar
    Join Date
    Aug 2010
    Gettysburg, Pennsylvania, United States


    they run on a switched ground. i would keep your fogs completly seperate from your headlights and then you can switch them on and off as you please
    03 Silverado 1500
    285/75/16 BFG's
    2 Blaupunkt 10" vW1000 subs in Subthump box
    ProComp Level Lift & 3" rear blocks

  3. #3


    That's fine if I have to do that, but it does not explain why my headlight is now dim. I need the answer to that, I can't be driving around with only one working headlight.

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