Dodgy brake light switch wires

Discussion in 'Technical' started by Tumbler, Jul 12, 2023.

  1. Tumbler

    Tumbler Member

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    I have something going wrong with my brake light switch. If one of the wires to the brake light switch touches another wire, the two wires will stick together and the insulation will start melting. I put a bit piece of some of that automotive wire tubing around it as a temporary fix. I've been doing a lot of other work to get my car up and running again. Just today on a test drive I smelled burning plastic, and the plastic from the connectors to the brake light switch looked melted.

    There was a disaster with the brake light switch in the past that happened when my dad saw that my brake lights weren't working, and he found that the one of the connectors was unplugged. I don't exactly know all the details of what happened, but I think he plugged it into the pin that was holding brake light switch in rather than the correct place on the switch. When I walked outside I saw the inside of my car was filled with smoke, and the insulation had been melted off several of the wires. He repaired it, but I'm not exactly sure what was done with the wiring.

    I thought there might be a short somewhere in the wiring due to damage from that past meltdown, but I disconnected the brake light switch wires, tested them with a multi-meter and I got 12 volts and around 5 amps. This certainly doesn't seem like enough power to cause things to melt. Could this be the brake light switch itself that's causing a short? My brake lights were full functional. Even when the plastic was melting.
     
  2. Krazy Comet

    Krazy Comet Tom

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    Requires more than 5A to melt wire insulation, probably there's a short in harness or to ground. I had a wiring to ground short at brake switch in my Cobra, harness burned all way back to head light switch. The supply to HL switch also feeds brake light switch. Luckily I had another harness on hand.
     
  3. Tumbler

    Tumbler Member

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    I just installed a new brake light switch and there's no more melting wires. The old was bent a bit and there was a scuff on the side. Other than that, it doesn't look too bad. A brake light switch usually lasts a few years on my car. This is the first time I've had the wires melt.

    (the old one is on the left)
     

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  4. jasonwthompson

    jasonwthompson Member

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    There are 2 washers and a bushing for the switch. Did you install them? I had problems with the switch until I did.
    [​IMG]
     
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  5. Krazy Comet

    Krazy Comet Tom

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    fordbrakesw.JPG I dunno how switches are sold these days(probably one size fits all?) but there are switches for power & manual applications. The power have a lighter spring as it doesn't require as much pressure to activate.

    Original sw has seen many hard brake applications. Notice how the activation plate is bowed on ends & banana shaped in center? Missing hardware will definitely aggravate this condition.
     
    Last edited: Jul 18, 2023
    mojo and dyent like this.
  6. Tumbler

    Tumbler Member

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    I'm definitely missing those washers and bushing. I going to have to pick those up somewhere. They didn't come with with the switch I bought. The shop only had one switch listed in the system. My car doesn't have power brakes. I think I may have seen power brakes in a Maverick before.

    The activation plate is certainly bent in the old one. I've had problems with the brake peddle getting very low. I've though that it might have had something to do with that. There's a slow leak in one of the brake lines. Another thing I'm getting fixed.
     
  7. Krazy Comet

    Krazy Comet Tom

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    The Mustang suppliers stock kits with all the small parts.
     
  8. jasonwthompson

    jasonwthompson Member

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  9. Tumbler

    Tumbler Member

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    Thanks for the info. Parts have been ordered.
     

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