Brake lights come on & off when vehicle is parked.
Already checked brake switch, and lights come on & off with brake switch removed. If it is a relay problem I can't find actual location.
Your brake light switch completes the circuit to ground and the lights come on. The positive side (+) is always hot on this circuit even with the ignition switch off. You have a bare ground wire touching something metal (unpainted) in the circuit. You'll have to trace the wires to find it. Start at the bulb sockets and work your way forward. HTH. - Jim
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