I know I have read it here, about using a cigarette butt to get the rpm sensor working, but I forget what exactly you're supposed to do. My nieghbor's '80 300SD's tach. isn't working. I fiddled with the sensor (black plastic cylinder) and it worked for a second then stopped. I tried the search function, but couldn't find it. Where do you stuff the cigarette butt?

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member