Updating should future searches find this. With the very helpful diagrams (thanks again @JK and @Revilla) we chased the problem down to the contacts on either side of the hazard switch. Remove switch, clean all contacts with emery paper and contact cleaner and all is now good, test drive and 24 hours later Suspecting a theme I also did same to the heated windscreen switch which now illuminates and draws power across the screen. Just need a warm, humid tunnel and mountain cool air to test. Not got one of those in the flatlands of MK so will have to go with the multimeter evidence. Views on replacing the switches?