You could disconnect the switch wires from the BCU
at the BCU
end. That would prove it was wiring if the problem went away. Drivers switch would still work, the rear one wouldn't.
I'll come back with the wire colour / pin number at the BCU
OK at the BCU
itÃ¢â‚¬â„¢s the middle connector, the one with 54 pins. You are looking for pin 39, blue green, and pin 40 green blue (main colour first, trace colour second). One is up, one is down, but I canÃ¢â‚¬â„¢t tell from the circuits which is which. Do one at a time, or make a note of which one is which otherwise you might get them back in the wrong holes and the window switch will work upside down.
If you disconnect these at the BCU
, then the problem is with the wiring between the switch and the BCU
. To isolate whether itÃ¢â‚¬â„¢s in the door, or further down the car, put the pins back in the BCU
and disconnect them in the door B pillar connector. Pin 8 Blue Green, pin 10 green blue.
You could also use a multimeter to check for short (or partial short) to earth. With the switch not operated, and the wires disconnected at the BCU
, there should be no reading between the wires and earth. If there is, that confirms a wiring problem.