rear courtesy light and silver relays
 

I have a 1987 420SEL and my rear courtesy light no longer works using the panel switch. It still works OK when you open the doors. I have tested the switch and it works fine. I have also checked the terminal where the switch plugs into and it's working OK. This problem just happened all of a sudden.
Second question, could somebody tell me what the silver relays are for in the fuse box. They seem to be designated by a letter. Is there any way to tell what each individual relay is for?
Any info would be appreciated. Thanks!

Change fuses in fuse box every 10 yrs. You should get the light back and the schematic is in the insde of the fuse box.