Why won't my Mercedes Benz 300D start when the radio and lights work?

Answer 1

I had the same problem. The fuse for the radio either needs to be cleaned or replaced I believe it is the third fuse from the bottom on the left side of the fuse box. It effects the relay in some way. I changed the fuse (which was not blown) and cleaned the fuse contacts, haven't had a problem since.

Answer 2

This can be due to any number of problems. I'm guessing either a bad starter or an ignition problem. Even something as simple as a dirty distributor cap can prevent ignition, and therefore prevent the engine from turning over. Your radio and lights draw their power from the battery, and are therefore not affected by the engine working or not.

If your car makes any clicking noises when you turn the key over, check your starter. Otherwise, take it in for a tune-up to get the plugs, distributor, etc. checked out.