I would also think a loose connection somwehere in the wiring could cause an intermittent bulb indicator. CHeck throughly with all lights on, including F/R fogs. I had one of the 2 lower-tail bulbs go out, and it missed my eye not once but twice!

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL