Take Gilly's advice-the rear side marker bulbs on w124s may be good but not lighting up; reinstalling the bulb can fix that. This was what I did today to check out why my dash light went on. Now its off and I'm happy.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)