Recently my Ingnition Switch was bad because I lost voltage to the Fan Blower and AC Compressor Clutch. I replaced the Switch and the Tumbler and the Steering Lock mechanism. If you replace the Tumber you may want to get a matched Tumbler from the dealer that matches your VIN and your current keys. My car was a '82 300SD and I posted the procedure what I did, just search under my ID. It can be done with the steering wheel inplace.

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1982 300SD