Curiosity got the better of me--took a look at the wiring schematic.

Dome light assembly is E15/4, contains 5 elements, dome light, reading light, and 3 seat belt warn bulbs. Also contains the switch and an electronic control circuit. (control circuit is denoted by a transistor symbol...) No relay is shown. Power feed for all light elements is fuse number 9, power feed for control circuit is fuse number 5. Ground is supplied from connection point W4. If there are relays involved in the function of the dome or reading lamp they are not shown on the schematic......

Send me a pm with your email address, I'll send you a PDF of the schematic.

J. M. van Swaay

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1994 E320 Wagon, 230,000 miles
1995 E320 Sedan, 106,000 miles
1994 E500 Sedan, 79,000 miles