Sunpro gas guage problem

[xaircav]

Untill I can afford the 5" guage set for my '53 5 window I'm using some sunpro guages to monitor the '62 283 under the hood. Everything works fine except the fuel guage. I hooked it up per the instructions using a sunpro tank sending unit (tank is a Classic Parts 20 gal.underbed). When I turn on the key the guage pegs to full and I know it is less than half full. Electrical is now 12 volts and I checked for good grounds. Same thing happens with the sending unit out of the tank manually raising and lowering the float arm.

[VetteVet]

This is the classic symptom of a no ground condition on the sending unit side of the fuel gauge. The gauge is getting 12 volts from the battery but no ground back to the negative post. If you can, run a jumper from a good ground to the sender side of the gauge and look for the gauge to go to empty.

when you pulled the sender from the tank did you ground the flange to a good ground?
test the sender with an ohm meter by connecting the leads between the center terminal with positive and the outer flange to negative. Then raise and lower the float and watch for a 1 to 90 ohm variance on the meter. If you get that then check the tank for a good ground to frame and the sender for a good ground to the tank. Then check the sender wire for a complete circuit to the sender side of the gauge.