I'm no MB Tech, but - Get the Anti-lock Brake System fixed?

If the light is on, there is something wrong. If code 29 is a speed sensor, then the top must think the car is moving, thus the top won't work.
Having one of these cars, I read all the tips posted here. I believe I read that where the speed sensors connect to the wiring harness, the joint can get corroded, causing problems. And I suspect if a speed sensor was bad or with a bad connection, your ABS would see a problem and would not function as well. So, take all the speed sensor connections apart, clean them shiny, and re-attach. If the ABS light goes away, I bet the top works.

Just a thought.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport