If you adjusted the duty cycle, it's a crap shoot as to whether or not any damage was done. You have no reference point in terms of what the duty cycle reading is/was both before and after your adjustment. Not a very scientific way to do things, really, but what's done is done. I would get yourself a duty cycle-capable VOM from Sears. I picked mine up on sale over the summer for half price, something like $30. You will pay many times that if you pay someone to diagnose, so I think it's a good deal.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280