I don't have a W124, but at least on the W123 card the radio is only listed once. Not sure just what that means, but I assumed that all of the radios needed the constant power as well as the switched power?!?

At any rate on 123's the radio is on fuse 4.

By the way the clock and hazard warning system is on fuse 2, so maybe that is where the constant power is supposed to come from. Fuse 2 is listed as a 8-amp, and fuse 4 is listed as 16-amp if there is a radio.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150