I have a 1979 300SD that had a ACC system that worked perfectly(yes even the ac) until two weeks ago. The heater motor had bad brushes (wouldn't run unless I tapped the side of the motor) I replaced it with a new unit from Phil.

It ran fine for a week then it blew #3 fuse. This is the fuse that control the ACC system.

I thought maybe the fuse was old, so I put in a new fuse and it lasted 5 minutes.

Any ideas....when it runs, it runs great but I can't keep #3 fuse from blowing

Thanks
Augusta