I have 1990 300E and the #3 fuse blew. Replaced it and guess what it? It blew again, DA! Checked the fuse designation slip at the fuse box and #3 fuse is for:
"parking/tail light right, headlamp cleaning unit (which I believe is the headlamp wiper), illumination: license plate, instrument, control element." I have eliminated by unplugging and replacing blown fuses all but instrument and control element. So I believe the problem lies in the instrument and control element. I hope this all makes sense so any advise would be greatly appreciated and thank you in advance.

Tim