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Thread: High beams not working properly

  1. #1
    Join Date
    Jul 2014
    Location
    Jacksonville, FL
    Posts
    84

    Default High beams not working properly

    Trying to figure this out while I work out my transmission issues. Low beams both work, but when I turn my high beams on one of the low beams shut off. Not sure where to start to try to fix but I have notice that this tan wire with white stripe is just dangling around not connected to anything. It comes out of the headlight harness loom just behind the driver's side headlights. Any idea what this goes to and if it's related? I can find any wiring diagrams that indicate what this could go to...


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    1988 K10 Suburban. 6.5L NA Goodwrench Engine: 506 block cast on August 12, 1996. Heavy Duty built 700R4. Full-floating 14 bolt rear axle. 3/4ton 10 bolt front. Brand new 305/75R16 Procomp AT Sport tires on brand new 16x8 steel wheels.

  2. #2
    Join Date
    Jul 2014
    Location
    Jacksonville, FL
    Posts
    84

    Default

    Figured out the random wire, it goes to the brake sensor on my proportion valve underneath the radiator. Got it plugged back in. Still trying to figure out the headlights though!
    1988 K10 Suburban. 6.5L NA Goodwrench Engine: 506 block cast on August 12, 1996. Heavy Duty built 700R4. Full-floating 14 bolt rear axle. 3/4ton 10 bolt front. Brand new 305/75R16 Procomp AT Sport tires on brand new 16x8 steel wheels.

  3. #3
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Arrow

    I suggest chasing/refreshing grounds to start. 1988 was a transition year model, meaning the "other than 1/2 ton" trucks tend to have features common to the before and after years. I don't recall if they had the "4-on" headlights, but I don't think so. If you have one low beam remaining on, it's probably been modified. Look for additional wiring with a diode between the hot wires connecting the beams. If one diode fails or loses contact, that low beam won't stay on.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  4. #4
    Join Date
    Jul 2014
    Location
    Jacksonville, FL
    Posts
    84

    Default

    Turned out to be a bad bulb. Put an indicator light on the power connector and it lit up. Swapped the bad passenger bulb with the good driver's bulb, and the good bulb still lit up (this time on the passenger side) but the bad bulb was still bad.

    But, I will say, I didn't see any modified wiring.
    1988 K10 Suburban. 6.5L NA Goodwrench Engine: 506 block cast on August 12, 1996. Heavy Duty built 700R4. Full-floating 14 bolt rear axle. 3/4ton 10 bolt front. Brand new 305/75R16 Procomp AT Sport tires on brand new 16x8 steel wheels.

  5. #5
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Arrow

    Bad bulbs are easily diagnosed and replaced. Still doesn't explain your original problem.

    Quote Originally Posted by AugustDiesel View Post
    Low beams both work, but when I turn my high beams on one of the low beams shut off.
    If the low beam worked, then didn't work with the high beam while the other side did, something else is amiss. Could be coincidental failure and a corrected poor connection while messing with it. Stranger things have happened.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  6. #6
    Join Date
    Jul 2014
    Location
    Jacksonville, FL
    Posts
    84

    Default

    Turned out to be a connector issue I suppose. Replaced the harness with a heavy duty replacement harness from LMC truck and updated the lights as well. Works great now!

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    1988 K10 Suburban. 6.5L NA Goodwrench Engine: 506 block cast on August 12, 1996. Heavy Duty built 700R4. Full-floating 14 bolt rear axle. 3/4ton 10 bolt front. Brand new 305/75R16 Procomp AT Sport tires on brand new 16x8 steel wheels.

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