got this 53 plate tdci mondeo estate coming in on tuesday with a strage fault. when the engine is running you can turn the side lights on ok but if you turn the switch a bit further to turn headlamps on the engine cuts out straight away. it sometimes happens if you have sidelamps on and pull out for fog too. if you turn the engine off and put the lights on and then turn the ign on the lights all work fine but 9 times out of 10 it wont start. my first thoughts are the switch but i haven't looked at it atall yet as it was getting dark when he called in on friday night and didnt have time to hang around for me to look as he would need lights to get home.
any ideas greatfully appreciated.