Look at the wiring diagram in the workshop manual and you will find a contact switch, much like a courtesy light switch for the doors operated by the light pod when they go away from the down position. There are in fact two of these on the LH pod, one for the light circuit relay and the other for the flasher relay. any malfunction could be caused by any one of these components or the wiring and connectors. Have a first look at the earth connections. It sounds a bit laborious but it is the only way involving a process of elimination to solve a lack of illumination.
I’d check the wires connected to the switches behind the dash too. Maybe remove wires one at a time, squirting electrical cleaner in the sockets one by one and sliding them back on. Or, it could be the switch itself, internally. Good Luck. Eric ps ; just re-read your description and I’ll add, I’d do the same at the headlamps, remove and clean the wire connection sockets.
I am sure I got 2 for my S4 from Sue Miller, if you have not had anything from her before she is most helpful. May be not exactly original style but they do the job.
I have now taken the original switch apart and found it was full of old hard grease. I cleaned it up and put a smear of new grease on, cleaned the contacts and put it back together all seems ok now.