I noticed recently the tail lights on my S4 won't go on and I think I've narrowed the issue down to the headlight switch, but I'm not totally sure. Are there any other known problem sources I should consider? My brake lights, headlights, turn signals all work as well, while the interior lights and the running brake lights don't seem to. Are there any other fixes I might want to try? Thanks.

Quick Edit: I have an NA, I'm not sure if that changes the wiring diagrams for the specific system but wanted to add just in case

 

Most certainly this is a failed headlight switch. Cold solder joints in the switch are the common cause, as are the relays. Additionally it is common for the harness connector to burn due to high resistance connections taking out both the harness itself and switch. If you pull the switch and find discolouration on the connector, that is the issue. The fix is a new switch and harness (1 foot harness which connects to the main harness).

Switch resoldering is covered in the 2nd gen FAQ.