I don't know if the bulb inside the switch is replaceable or not. It surely can't be much of a bulb, must be smaller than the tiny bayonet bulb for the shift indicator. Probably best to simply replace the switch.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.