On the 96 C280, we had an intermittent wiper and turn signal problem. First thought was the combination switch, but that was fairly new. I searched this forum and found test procedures that focus on the relay, which IIRC, controls the hazard flasher and rear defroster as well. The tests helped me focus in on the relay, which was the problem.

Some people call this the "combination" relay, others call it "wiper", and it may have other names as well. I got a good price on mine from our sponsor here. Fastlane calls it the "Multifunction" relay (navigate Body Electrical-Relay-Multifunction for your car). I hope this turns out to be your problem, because it is the easiest, cheapest thing to repair.

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1996 C280 289K Traded
1997 E420 167K Traded
2001 S430 240K Traded
2010 E550 4matic 80K
2000 GMC Jimmy 198K Gone to Boneyard
2003 Camry LE 196K
2011 Mazda3 i Sport 31K