How does the sending unit work? My gauge has been a train wreck from day one. And today, with well over half a tank indicated, my reserve light started to come on/off for a few miles until it was steady. Then my needle dropped to a quarter tank. A few minutes later, it showed over half a tank again. But the reserve light stayed on.

So should I remove the sending unit for a cleaning. I just ran B12 through the car. Or is it the dash gauge that is bad - which is what I think it is.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car