When I flash the headlights ??

on my p38 dse when i flash the headlights the stereo goes out and it takes about 30 seconds for it to reset itself as anyone got any ideas what it could be its still got all the original wiring in place none has been chopped etc and its been ok for nearly 2 years and only just started doing this

Could it be something to do with the stalk switch affecting the streering wheel radio controls???

check all your earths tooooooo

got no radio controls on the steering wheel and had done all the earths and the becm connectors and the connectors in the footwells about a month ago

bad battery is my guess how old is it mine did this just before it died, odd how it managed to start the car but not run a radio and full beam.