I have a 1984 Mercedes 380SL with the original Becker Radio. The radio works fine except when you turn on the headlight it goes off. Anyone have any ideas why.

 

The same thing happened with my '76 450SLC. My alternator couldn't keep up with the load added by the headlights, the voltage dipped causing the radio to cut out. First check the brushes on your alternator. If they are short, replace them. Most auto parts shops (NAPA, Schucks, etc) have a machine to check your alternator. If the brushes don't bring the voltage up to where it should be (~14 volts), then try the diodes or voltage regulator. Ask the parts store for recommendations.