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Q: installed wire harness kit causing brake lights to stay on trailer and causing brake lights on car not to work

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I installed a wire harness kit into my car and connected it to my camper trailer. The running lights and blinkers work, but the brake lights on the trailer are always on. I disconnected everything then reconnected it and tested to see if it would work properly. It didn't work right for long - only 10 minutes. I checked the pin voltage at each pin of the 4 pin connector and got 12 volts when the brake pedal is not applied. Now my brake lights on my car won't work including the top brake light. Did I somehow cause something to short out?

Hello there, it sounds like something may have shorted out. The brake switch system can only support so many amps of power, and with the addition of the trailer lights, it may have exceeded the capacity and caused the fuse to blow. Most likely the trailer brake is wired wrong or has exceeded the capacity of the system it was attached to. A qualified technician such as one from YourMechanic will be able to diagnose your brake lights and perform any repairs required.

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