1970 Swinger Rallye Dash gas gauge stuck on 1/4 car on or off

here's how the gages and sender work.
Thermal-Electric Gauges (Session 227) from the 1966 Master Technician's Service Conference

And the filmstrip that goes with that, along with a pdf version of the booklet at
Browse MTSC by Model Year – 1966 – MyMopar