Are you sure that the switches are no good..(since the control light is working).
Just dive underneath the seats and try to find power at the heater plugs with a test light.

If the control light is illuminated, the switch does hand over the power...

...just a thought...
greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)