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Brake Light Fuse Blowing

Discussion in '80-Series Tech' started by mikray55, Apr 29, 2012.

  1. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    '96 Eighty

    My brake light 10 amp fuse will not hold.
    Removed portion of after market trailer harness.
    (will remove the remainder as soon as possible)

    The fuse block slot where the 10 amp fuse inserts is visibly burned on the power (battery) side of the fuse slot but not the load side.

    Anyone have any thoughts as to whether this makes the problem worse?

    Thanks!
  2. Offroads4x4

    Offroads4x4

    Messages:
    1,292
    Location:
    SLC, UTAH
    No question you have a short. Yes you need to clean the burt area the best you can. Be sure to always use dielectric grease on all you electrical connections to help your connections continuity and keep it from burning/blueing.

    Start by looking for the obvious like you've done on the trailer light wires. Next check your hatch wires for the third brake wires.

    Then check each tail light socket and replace each bulb. I've seen cheep ones short out. Checking the wire looms for the rear lights paying close attention to the area where the wires go through the body.

    Then report back.
    Last edited: May 6, 2012
  3. scrowley

    scrowley

    Messages:
    2,164
    Location:
    N. West CT.
    This happened to me and it drove me crazy!!!! It was a dead short......and it ended up being a wire on the aftermarket radio that was not used and not capped or taped but just cut off flush was touching something in the dash causing the short. Before I figured this out I checked all lights and light sockets in that circuit. Checked all wires for towing harness. Have you installed a aftermarket radio lately??
  4. nuclearlemon

    nuclearlemon not an addict Moderator

    Messages:
    14,314
    Location:
    meh-ico, colorado
    for anyone who finds wires like this, just grab a butt connector and crimp it on the one end and leave the other end open. easy way to leave it open for something in the future and keep from shorts like this. if it's in an area where you're concerned about water/dirt getting in, you can put a vacuum cap on there (or skip the but connector and use a piece of heat shrink). also, please don't be a p.o. and use checker auto butt connectors, use a quality heat and seal style connector ;)
  5. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Will do Off Roads, Thanks
  6. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    No radio replacement. Probably rule that one out....
  7. 86tuning

    86tuning

    Messages:
    2,557
    Location:
    Vancouver BC
    quick and easy diagnostic tool is to make a test light using a 12v bulb and a couple wires. plug these wires into the fuse socket, then start unplugging stuff until the lamp goes out.

    first thing I would check is the tail lamp and brake lamp bulbs. next would be the trailer wires.

    good luck!
  8. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Hey 86tuning
    I am going to check out the brake lamps and trailer harness real close. But if I use the temporary test light that you a suggesting, won't that act as a "straight wired non fuse " situation ?
    Thanks
  9. wesayso

    wesayso

    Messages:
    205
    Location:
    hampton, VA
    When this happened to me it was the trailer lights module that was bad. Replaced it and everything was cool. Replaced the module with this.
  10. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Update - before the fuse blows I'm pulling 14 mAmps on the 10 mAmp protected circuit. So still got a short somewhere. Removed trailers harnesses.....
  11. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Here's the wrap up for now:
    1) Removed 2 after market trailer harnesses.
    2) Got the fuse to quit blowing by bending each tab of the 10 mAmp fuse in opposite directions for secure insertion.
    3) Still drawing 14 mAmps on the circuit but the 10 mAmp fuse is holding. Must still be a stray ground somewhere, good , bad or evil...

    Weird thing is: the fuse "holder" on the fuse block is a bit smoldered from the earlier melted fuse. I understand that this causes higher resistance and therefore ups the current amps at that point. But the 10 mAmp is holding.............

    I guess I will go worry about something else.....

  12. 86tuning

    86tuning

    Messages:
    2,557
    Location:
    Vancouver BC
    Nope.

    What happens is your 12v bulb is the 'load' and will light up brightly until you find and remove the short circuit.

    Once you unplug the cause of the short, the bulb will go out.

    There will be no damage to anything unless you manage to mangle up the fuse socket, or allow the bulb to melt carpet or similar.

    I use a turn signal/reverse bulb 1156 with pigtails soldered to it. 18g stranded wire can be carfully plugged into the fuse socket. Or if you have some spare toyota connectors laying around, you can un-pin them from the plug and use those. I've cut faulty 02 sensor plugs off and used those terminals. they work great.

    hope that helps. You'll find it. Most likely culprit is the trailer connector, or melted tail lamp bulbs causing a short.

    Good luck!
  13. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Ok 86 - will keep this deal open and chase the culprit and report back
    Thanks!
  14. Scamper

    Scamper

    Messages:
    1,460
    Location:
    Somewhere in NJ
    When you removed the two (?) harnesses, did you find a wire going up into the tail light? If the PO had a trailer with surge brakes, he may have wired the reverse light to his surge brake wire and this may be loose or shorting on something.
  15. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Hey Scamper
    Yes the right tail light has a t connector with no wire protruding on two of the wires inside the lens. Still chasing.....
  16. Offroads4x4

    Offroads4x4

    Messages:
    1,292
    Location:
    SLC, UTAH
    Have you checked under the dash at the brake light switch on the brake peddle? Most of the time people jump one of the switch wires for the trailer brake/surge brakes.
  17. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Hey Offroads,
    Good point, I did checkunder the brake peddle, but not necessarily for additional wires......still chasing.
    Thanks!
  18. Offroads4x4

    Offroads4x4

    Messages:
    1,292
    Location:
    SLC, UTAH
    Try unplugging the left tail light and see if it still blows, then try the right one to eliminate your sockets and the socket wires.
  19. mikray55

    mikray55 SILVER Star

    Messages:
    405
    Location:
    NC
    Well now the circuit is not blowing. If is just continuing to carry 14 mA on the 10 mA fuse....

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