> The gas gauge in my 79 bonnie all of a sudden wil not work anymore
> it flew up past a ful tank and just lies fla and doenst move.
IIRC, if the signal wire going back to the tank gets disconnected anywhere (i.e. open), it'll peg the gauge on Full as you describe. By comparison, if it shorts to ground, I _think_ it will peg on Empty instead. So I would trace that wire to the back and check that it'* got voltage going all the way back.
It runs through a main bus cable of about six solid-aluminum wires from the vicinity of the fusebox under the dash, under the carpeting on the floor, through the left front corner of the trunk and down to a connector in the lower-left corner of the trunk, where it connects to a regular stranded-copper wiring harness.
I think the wire you're interested in testing is Tan color; others you should find are Dark Green (right brake/turn), Yellow (left brake/turn), Brown (taillights), Light Green(?) (Backup?) and maybe Orange (constant hot).
Check that the wire has voltage up at the fusebox end, then at every point along the way where you can reach it, including going out through the back of the trunk and into the top of the gas tank. Try unplugging the main harness connector in the lower-left of the trunk and verify that you've got voltage back there when the ignition is on, and see where that leads you.
-- Andy Green