Few possibilities: Is this a UK spec car? Has it just started doing this? If yes and yes, case of getting wiring diagram and working back through the circuitry with a multimeter. Done it on a 405 and found lighting fault due to a break in the wire cutting the feed to the relay. However, if one wire is broken, whole loom is normally quoted as a replacement. Lot easier to get an autoelectrician to do this. Otherwise may have to replace some of the relays or resolder ignition wiring if not UK spec. S.

I have had the EXACT. same problem problem on my R reg 306 turrbo diesel with electric windows and sunroof. Found out this morning that the passenger side electric window switch was back feeding to the side lights. I fitted an incorrect or faultysecond hand switch a couple of weeks ago and that is when the fault occurred.