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No headlight or marker lights

Discussion in 'Electrical & Audio' started by Spencer hastings, Apr 13, 2021.

  1. Spencer hastings

    Spencer hastings Junior Member

    Posts:
    4
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    4
    Joined:
    Apr 13, 2021
    Location:
    Westfield ma
    First Name:
    Spencer
    Truck Year:
    1985
    Truck Model:
    C2500
    Engine Size:
    V8 350
    Hello I have a 1985 gmc c2500 v8 350 I recently had my 700r4 rebuilt it crapped out . Then I fired it up and heard tapping . Under valve cover . Long story short had to replace cam Tapp lifters and wile I was doing that noticed someone pit 305 heads on it replaced with 350s broke in went well tuned carb up and when I went to drive her for the first time after fixing all of this I noticed I did not have headlights nor do I have marker lights . Broke out the prob and multi meter. All grounds are comming out good . Fusible link are showing up hot . Checked headlights with my probe and headlights light up so they do work got under the dash looked at the switch red wire is always hot as should be all fuses look good. But with it all looking good I'm not sure wear to go to now . How many grounds are their for the lights on my truck I got 3 up front off of wiring harness for headlights . I got one on pass head to frame battery to frame and I got one under the dash on driver side by the switch did I miss any? I'm thinking switch because all the wires.and grounds check out good. Not sure what elts it could be . Brake lights work reverse work blinkers work no headlights high or low and markers. What u guys think im lost on this one
     
  2. Shorty81

    Shorty81 Baby Boomer

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    First Name:
    Darren
    Truck Year:
    86
    Truck Model:
    K20
    Engine Size:
    496
    Welcome from the Buckeye State.
     
  3. Matt69olds

    Matt69olds Full Access Member

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    Joined:
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    Location:
    Central Indiana
    First Name:
    Matt
    Truck Year:
    81
    Truck Model:
    GMC 1/2 ton
    Engine Size:
    455 Olds
    Find the connector for the dimmer switch on the steering column. There will be a green wire (high beams) tan (low beams) and either a yellow or blue wire which is headlight power from the headlight switch.

    Turn on the headlights, check for power at the dimmer switch on the yellow or blue wire. If you have power, check the green/tan wire, you should have power on either of those wires depending on the position of the dimmer switch. If everything test good there, your headlight problem is between the headlight dimmer switch and the front of the truck.

    No power at the dimmer switch? Remove the headlight switch. There is a tiny button on the headlight switch that needs to be pushed and held down while removing the switch knob. Once that’s out, unscrew the retaining nut. When that is out, check for power on the red wire, that’s power from the fusible link to the headlight circuit. If you have power there, but nothing on the yellow/blue wire with the headlight switch on, replace the switch.


    While the switch is out, check for power on the orange wire. That’s power from the fuse box for the tail lights. If you have no power there, double check the fuse.

    If you have power on the orange wire, pull the headlight knob. You should have power on the brown wire, that’s the taillight circuit feed. If you have power on the orange wire, but nothing on the brown, replace the switch.

    You could also use a FUSED jumper wire to bypass the switch for testing purposes. If you jumper the red wire to brown, the parking lamps/taillights should come on. Jumper the red to yellow/blue, the headlights should come on, abd you should be able to switch from high to low on the dimmer switch.

    Just make sure you have a fused jumper wire before attempting to bypass the switch. Their is a circuit breaker built into the headlight switch, if the breaker has tripped and failed in the off position, then something is seriously messed up in the headlight wiring. No fuse in your jumper wire might let all the smoke out of the headlight wiring.
     
    idahovette likes this.
  4. idahovette

    idahovette Full Access Member

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    Location:
    Weiser Idaho
    First Name:
    Perry
    Truck Year:
    1975-1979
    Truck Model:
    K20-K10
    Engine Size:
    350
    @Matt69olds is correct, never let the smoke out of the wiring, only tire smoke is good!!
     
    82sbshortbed likes this.
  5. Scott91370

    Scott91370 Full Access Member

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    Truck Year:
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    Truck Model:
    Sierra1500
    Engine Size:
    350
    Throwing this out there.

    If it is all front end lights check the bulkhead connector on the firewall. They are all on one central mounting point.
     
  6. Spencer hastings

    Spencer hastings Junior Member

    Posts:
    4
    Likes Received:
    4
    Joined:
    Apr 13, 2021
    Location:
    Westfield ma
    First Name:
    Spencer
    Truck Year:
    1985
    Truck Model:
    C2500
    Engine Size:
    V8 350
    Update

    I figured it out guys so when I pulled the tranny out and brought the starter down one of the wires popped out and I put it back on the positive thermal and poof headlights and markers are back. Thanks for everything
     

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