Look on the firewall, not sure which side on your car (it's near the master cylinder on the 560). You'll be looking for a silver module with a red top, it also has a clear flip top - very distinctive, only one like it. Under the clear flip top you will have one (possibly two if the unit has been changed) 10amp blade type fuse. Check the fuse it may be blown, if not spring for a new OVP ~$50.00 or so.
'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.