Possible causes of fault

'Short circuit to B+' Continuous lighting of auxiliary headlight bulb(s) can only be diagnosed when auxiliary headlight is switched off.
'Short circuit to ground' Failure of auxiliary headlight bulb(s) can only be diagnosed when auxiliary headlight is switched on.
'Open circuit/short circuit to B+' Continuous lighting of bulb(s) in the event of a 'short circuit to B+', can only be diagnosed when auxiliary headlight is switched on.
'Open circuit/short circuit to B+' No lighting of bulb(s) in the event of a 'disconnection', can only be diagnosed when auxiliary headlight is switched on.