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Thread: 1994 silverado brake light issues

  1. #1
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    1994 silverado brake light issues

    Hey,
    I am new to your forum. I have looked through some of the threads but did not find my answer. I have a 1994 silverado mark III with no brake lights at all. I replaced the switch, checked the rear with the meter. I do not have power at the fuse. Sometimes it does and sometimes it dont. Even when it does I dont have lights. Where does the power at the fuse come from? I could really use a schematic...

  2. #2
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    Welcome to the forum Jethro.
    I have a 94 Silverado, never heard of "mark III "

    Fuse is a very good place to have power. Not Brake fuse, but Stop fuse.
    Stop fuse supplies ABS, Haz flasher, brake switch(to brake lights and cruise),
    and convience center(to chime alerts for key/lights)

    Fuse is supplied from a fusible link connected at battery junction block on firewall.
    That passes through bulkhead connector and, after a splice, goes four ways.
    One to Stop fuse, one to ACC-BATT cb(lower silver can) for pwr locks, two to key.
    .
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    Last edited by crabtruck; 04-11-2010 at 12:07 PM.

  3. #3
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    what now

    OK. I have power now. The brake switch has power to one terminal (pink) all of the time and power to one terminal (purple) when the pedal is not depressed. When the peal is depressed it connects between the orange and yellow wires and disconnects between the pink and purple. I can use a jumper and get the brakes lights to come on by jumping between the pink and yellow wires. This trips the relay and all brake lights work. I tried plugging in a new multifunction switch and no diference.

  4. #4
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    The Mark III is just one of those conversion deals. It had an alarm on it at some point which has now ben totally removed to make sure that was not a problem. I figured out why my power was coming and going. The fuse only has power with the key in the run position. Dont know why though.

  5. #5
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    You are talking about this like it is all one switch and brake circuit.
    It's not and you should not cross wire while testing.
    You will have less chance doing so if you leave the key out,
    you don't need it for brake lights anyways.
    There are actually seperate switches working the opposite way
    (make or break connection) when pedal is pushed.
    Pink should not be hot at all times, only with key.

    What you want is to have a hot at all times on the Org wire
    which comes from Stop fuse.
    When pedal is pushed, hot should appear on Yellow wire.
    Since you say you have brake switch good connect Org to Yel,
    and you say making the Yellow "hot" makes lights work,
    it sounds like Org is not hot.
    Test again with no key and see what's hot when.

    Does HAZ work when brake lights don't ?

    Note that a bad multi function switch on column won't stop 3rd light
    shown along green arrow in drawing.

  6. #6
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    You are looking at wrong fuse (Brake), you want the STOP fuse.

  7. #7
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    OK we are getting closer. With the key off I have no pwer at the switch or the fuse. The hazzards do not work either I just thought that was the flasher that I have not found yet...

  8. #8
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    Are we on the same page as to which fuse ?
    The green fuse - not the red one.
    .
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  9. #9
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    Fixed

    I thank you for you help. I could not read the fuse block where it said STOP. I feel like an idiot but thank you. At least got all of the old alarm system wiring and **** out of the way now.

  10. #10
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    Fuse was blown ? Replace = good to go ?
    Great news. Thanks for letting us know.
    You'd be surprised how often little stuff like that makes folks nuts.
    Worse in this case, since the wrong fuse says the "right" thing.

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