Recently my 91 300E's doorlocks stopped working when turning the key in the driver's side to autolock and to unlock all doors (also the at the trunk). At the same time, my radio would almost turn on but then it would shut off...no numbers or readout would show on it. I thought that I either had a vacuum leak for the doorlocks or the pump had failed. I also thought the radio had had it at the same time. From reading through these threads I checked fuse "C" and lo and behold, all was still good! The contacts on the fuse had oxidized so bad there was no contact. I scraped both ends on the sidewalk to make it shiny and new and both issues were immediately fixed! Just thought I'd throw that out there as I almost went and popped for a new radio head unit and was about to tear apart my seats for a vacuum leak or bad hose connection. Cheers!