Unless these cars are much different than the 129 SLs, electronic top controller could also be at fault. Has it been replaced/rebuilt?

The top will do funny things if it's not getting enough voltage. Perhaps the car sat too long, and the battery is drained or old?

Lots of variables here. Either verify repair history, or start by checking battery and alternator. If checks out, check for leaks and check the switches as Don suggested, using his instructions.

It's got to be one of those

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

current: 08 C300 Luxury , 92 500SL