fuel gage way past full

[smoke]

have a 85 gmc.just getting it running.bought it with a bad hg and turned out it sit to long and froze the motor up.so now i put a new motor in it.and fuel gage reads way past full.no matter what tank you select.switch in dash?any help would be sweet.thanks

[joesgarage71]

 Check the ground wire from the tank sending unit to the frame. Make sure you have good clean ground.
 Steve

[VileZambonie]

Way past full = open circuit (high resistance) Pull the wire that goes to the gauge and ground it. It should go to E... If nothing happens try tapping on the gauge and see if it moves. If nothing happens you'll have to pull out the cluster to check it.

[smoke]

any help on wire is the ground for the gage?you can hear it switching tanks.but the gage doesn't move.i will tare the dash apart so i can get to it.thanks

[75??? franken-trunk]

i had the same problem in my 75 3 years back i cut the wire and ground it to the frame but nothin happened cuz i did it after the break in the wire, it just happend one day so a year later i went back at it, it was melted or something the exsaust... so check there first, i wouldn't tear into the dash just go underneth and trace the wire(s) mine was pink

[joesgarage71]

 Brown

[79gmc1ton]

I noticed you said you just replaced the engine. check to see if the ground from engine to the body is there. sometimes gauges will not work right if the ground is not there.

[smoke]

Gauage moves when you ground out the pink wire with the test light.ok here is what i did.i took the dash apart.and when i ground the pink wire with a test light the gage moves.i took the plug off of the valve under the truck.and the two pink wires one was bright the other dim.guessing one has more gas than the other?and one had constant power.any ideas what next? ???thanks

[VileZambonie]

go right to the source. pop the wire off of the sending unit u are switched on to and ground it. Observe the gauge. Then flip the switch and do the same thing. Observe the gauge.

[smoke]

k.and then what?bad ground?

[VileZambonie]

see what happens...if it functions correctly at each tank when the switch is flipped to the appropriate tank the only thing that's left is the sending unit and or it's connections.

[smoke]

ok today it off the driver side tank.hooked another sending unit up.and it did the same thing.checked the ground and cleaned it.after i put it all back together.i went in the cab and switched tanks.now if you switch it just rite the gage will work.rite now i have the right side working.driver side goes to like 5/8 and i don't think that is rite.sometimes you have to switch it 2or3 times or it will just go past full.wouldn't do this before.you could mess with the switch all day and it wouldn't move.