All you have to do is replace your front door switch with one from a W210 car's trunk light, which can be pulled out to turn off whatever the switch normally turns on. The part number is 201-820-21-10 and no doubt other Benz cars also use that switch, you might get lucky and find one in a junk yard.

With the switch installed, open the door, turn the key to position 1 and get the annoying buzz. Pull out on the switch pin, it pops into place and the noise stops. Now turn on the radio and enjoy.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970