1947 Cadillac Erratic Gas Gauge

[bill_boos]

Gas gauge stays pegged at full while driving. At stopped, it bounces between half and full.
This with about 1/2 tank of gas. Should I be looking for a gauge problem, sending unit or . Anyone ever seen or heard of this problem and how to diagnose?

Thanks, Bill

[Bob Schuman]

Very likely that it is a problem of a bad grounding of the sensor in the top of the tank. Run a new ground wire from one of the five sending unit mounting screws to a place cleaned and shiny on the frame, which should fix it. The sender is very difficult to access from under the car with the tank in place, but on some cars a previous owner has cut and access opening in the trunk floor  and covered it with a homemade plate. That makes sender access very easy.