When I got the car the mirror turn signals were working but I just noticed that the driver's side wasn't working. Upon further inspection, the door wiring harness was also broken. I also had this on the mk3 Passat TDI. Supposedly the early mk5 Jetta were bad but hopefully they improved this on later cars. The repair is to solder new wiring or replace the door wire harness. Why they can't just use higher quality wiring for at least the door harness, I don't know. The insulation cracks and in bad cases, the wiring also breaks. It breaks because it bends back and forth when the door is moved. PITA. Pics and procedure to fix to come later.