look at the electrical diagram for your car (get a CD if you don't have one, see ebay or FastLane) and see if any of the failed components are on a common ground or common voltage path.

Consider a bad ground and thus the need to reground. As these cars age, the components become noisy, wires brittle, etc. Sometimes it's difficult to maintain a good ground. So regrounding the circuit somewhere else on the chassis can help.

Look for something ungrounded in the car. Per other poster, look for no ground/bad ground at antannae for example. Look for loose wires for any car components you can easily get to.

If you have other assorted electrical problems, consider the over voltage protection relay (OVP) which is located behind the glove box on the 380SL, I think the same on yours.

If you can't get to this at the fuse box and can't find a bad ground somewhere in the car (e.g. as suggested by another poster) then you need to start removing things (radio, etc) and go in there with a multimeter and start to trace it out. You need to be able to verify good ground-- do that by measuring for continuity between a ground on the chassis (put one lead of the multimeter there) and on the ground wire coming into the radio. All multimeters have a simple continuity test mode. If the multimeter beeps and says continuity, the ground is good. if not, it's not. Then using another ground verify voltage to the radio. Use this method troubleshooting through the system. If for any reason you choose to measure current, you do that IN SERIES with a +volt wire (e.g. between a device and the wire offering +12 volts). Do not put the multimeter in current mode and then try ot measure current betweeen +volts and ground. That's shorting out +volts to ground, bad.