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Brake lights - no power to switch

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  • Brake lights - no power to switch

    After a shop did some welding on my car, the airbags went off and my brake lights no longer work.

    I narrowed the brake lights down to no power at the switch connection. From what I understand, one of the two terminals going to the switch should have power. There are two switches, a black and blue. Neither have power to any of the terminals.

    I even disconnected the wiring at the rear seats (there is a bulkhead connection near the rear speaker) to try and isolate that wiring. Mainly because I have the hitch lights back there and I didn't want to undo it.

    Fuse is good, running lights work. No brake lights.

    Any help is appreciated.
    Chicago Region SCCA SM # 688 http://www.scca-chicago.com
    TSSCC SM # 688 http://www.tsscc.org

  • #2
    (how do airbags go off after a shop works on the car)

    My mind is dusty, but doesn't the 4 way button sometimes make issues with the tail lamps?
    'Slicks on a car show me you care - broken axles show me you're trying'
    [I]Nitrous Rental Cars - Turbo Festivas - Vehicular Lunacy[/I]
    [SIZE="3"][B][url]www.sloppymechanics.com[/url][/B][/SIZE]

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    • #3
      I have heard that welding without properly grounding the car can do some funky things to the electronics. I may be off base on this one but after the welding, my brake lights didn't work and my airbags went off on me for no reason. Seems electrical.
      Chicago Region SCCA SM # 688 http://www.scca-chicago.com
      TSSCC SM # 688 http://www.tsscc.org

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      • #4
        I don't *believe* that switch is supposed to have power on it. grab your wiring diagrams out of the FSM.
        IIRC, one side of that switch goes to ground, and the other side goes to the tail lights. thus you might see 12V on that side of the switch wiring until you push the pedal down- then it will close the circuit and both sides will be connected to ground.

        anyway, where were they welding on the car? I'd look in that area for any burns on the wiring harness.

        I've welded on my cars literally hundreds of times and have NEVER had anything electrical go bad. think of how many muffler shops weld exhausts on cars and they never do anything to the electrical system.
        Originally posted by SoSideways
        I don't care what color they are as long as they are LONG AND HARD.
        '04 G35 Sedan 6MT- The DD
        '96 240SX- The Track Toy

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        • #5



          I tried a test light on both leads and nothing. I also tried to jump one to the other and nothing. I didn't jump the pins from both switches at the same time though. I don't under stand why there are two switches.
          Chicago Region SCCA SM # 688 http://www.scca-chicago.com
          TSSCC SM # 688 http://www.tsscc.org

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          • #6
            Not super familiar with the wiring on these cars but maybe the second switch is used on automatic-equipped cars to let you shift out of park. Or it is an ignition switch that has to have the brake pressed to let you start the car.

            Either way it looks like the r/y wire going to one of the switches needs to be hot when the key is on.
            If no power there but the fuse has power and is good (ie power is going through it) obviously the prob is between the fuse and the switch on the pedal.

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            • #7
              I think I have it all figured out, sorry to post such a simple one. There is a fuse for stop lamp. Unfortunately that is rubbed off of my fuse panel diagram so I didn't see it. I tested all the fuses and they all were good but I'll just take 12 volts, put an inline 10 amp fuse on it and put it to the r/y wire on the brake switch. Should solve it.
              Chicago Region SCCA SM # 688 http://www.scca-chicago.com
              TSSCC SM # 688 http://www.tsscc.org

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              • #8
                It should. But I'd try to figure out where the prob is. You could have other, potentially future, issues.

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                • #9
                  OK, yes.. the R/Y wire should have +12V on it, and the R/G should have a connection to ground. Since it's through a pair of 25w bulbs in parallel (50w total load, that's ~4A of current, R=V/I, so R~3 ohms.) You should see ROUGHLY 3 ohms to ground on the R/G wire on the connector if both of your brake light bulbs are good.

                  If you don't have +12V on the R/Y wire, then you need to find the problem, not just hotwire the thing to get +12V back. That's how fires start man..

                  Hell, your car already exploded on itself just by driving. Doesn't that tell you there's an electrical problem?

                  I would venture to say there's soemthing FUBAR on your wiring in/around the steering column. your brake light wiring only comes 'somewhat close' to the airbag wiring, but both are having problems. it would be good juju if you started looking for the source of the assplosion before you assplode something else.
                  Originally posted by SoSideways
                  I don't care what color they are as long as they are LONG AND HARD.
                  '04 G35 Sedan 6MT- The DD
                  '96 240SX- The Track Toy

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                  • #10
                    This may be beyond my capabilities. Do you think there could be a short somewhere causing this? Why doesn't the fuse blow if it is a short?
                    Chicago Region SCCA SM # 688 http://www.scca-chicago.com
                    TSSCC SM # 688 http://www.tsscc.org

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                    • #11
                      Not a short as that would pop the fuse. Just a cut or broken wire. But other wires in the same area could have been compromised in the same manner and might give you problems later

                      It's not a far run to trace just check for power off the fuse and head to the switch until you find the prob/don't have power any more.

                      Or start at the switch and work upstream.

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                      • #12
                        Chances are something/one cut into some wires which included brake and airbag. The airbag wire was grounded or shorted into another wire is my guess

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