OK, I got my 74-2.0 on the road after what was probably 6-7 years parked (3 with me) I had about 1/8 of a tank of fuel when it went for its MVI and after it passed I went to the gas station and put $25 in and now the gauge needle swings wildly from side to side.

Tank sender?
Ground?

The float rides on 2 thin copper wires within the the sender. Sounds like the float jumped off one of the tracks. It's an easy repair, after you pull the sender.