Quote:
Originally Posted by Seeker
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Since the tail light is fed with 12V I would have expected the brake light voltage to also be 12V when one or other brake switches are activated and 0 when they're not ...
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Quote:
Originally Posted by TamSV
Worth double double checking it’s not jammed on. If the white/black is the brake then shouldn’t it be zero without either of the switches activated? (I would have thought - guessing though)
Can you disconnect both brake switches altogether just to be certain? ...
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This, IMHO too.
From glancing at my K5 wiring diagram, it should be straight 12V (i.e. battery voltage) on the White/Black wire when either switch is pressed on (White/Black is the brake light feed from the switches), and close to Ov when off
It's possible the tail light internals have failed (even LEDs & electronics break down from time to time) but unlikely, as you say, so I suspect a corroded or otherwise gummed up switch. I can't recall how easy it is to disconnect them but that's what I'd be looking to start with: Disconnect both and reconnect each in turn to see if you can isolate the fault. Test each switch with a multimeter if you have one.
From memory, the switches aren't really dismantleable for cleaning but sometimes you can get away with spraying lots of cleaner into the switch via the operating stud and operate them many times to try to dissolve or wash away any crud inside on the contacts, but often it's pretty much replacement time if they're not on/off binary clean.