When the door is open and you turn on the ignition, the dome light will flash. I've never seen a Mercedes explanation of this but suspect it is designed to tell you you've got a door open. The light shouldn't flash once the door is closed. Possibly there is a fault in the light circuit making it sensitive to the lower battery voltage caused by the drain of the starter. Try popping the light/switch panel out of the overhead and checking for good connections at all points including ground.

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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