When I bought our Euro 300D, the dome light switch was broken, so the dome light remained dark. Rather than spend the bucks for a new fixture, I retrofitted a SPDT rocker switch in the space vacated by the rotary switch. There's no light in the car as I walk away, and I have to leave the door open to find the right key, but the rocker really rocks otherwise.

Phil
'84 Euro 300D, dome light really rocks
'85 300D, OEM dome light