56 Fuel gauge problem

My recently purchased 56 Chevy has a new tank, sender and wiring harness.The problem is the gas gauge doesnt work.If i tap the dash with the palm of my hand above the gauge cluster the needle on the gauge will jump from below empty to past full ,but it stays there until you run out.Should i suspect the gauge or the sender ? Maybe a bad ground? The wires are hooked up on the gauge and the tank properly ...

 

If the sender wire is not connected, or the sender has an open circuit in it, or the sender is the wrong one (wrong resistance), the gage will read past full. If the sender wire is shorted to ground, it will read empty (not past empty). If the gage is not getting power, it will read past empty.

It sounds to me like you have two different problems...

 

My brand new sending unit had several cracks in the float. Made the gauge act goofy. Also, might make sure they didn't put rubber padding between the tank and the floor or between the straps and the tank. That's how the tank grounds. Just some thoughts. Good luck.

 

Okay ,i just went under it with a flashlight and the wire had pulled off the sender on the tank.I hooked it up and now the gauge reads past empty until i turn the key .It reads empty exactly with the key on.If i pull one off the wires off the back of the factory gauge with the key on ,it will drop to past empty.I guess this means the gauge is gettin power now.I know its full cuz i filled it to the brim about ten miles ago.Now what do think is the problem ? I can tap the dash all i want now and it doesnt affect the needle ...

 

I had a simmilar problem withmy 56. It just ended up being a bad ground. Up in the rearend hump on the drivers side you'll see the grounD wire for the tank. Wiggle it loose a little or take off and clean the connection and screw back in. No worries.

Brian

 

pull the wire off of the sending unit with the key on it should read past full ground the wire & the gauge should read empty place test light between the sending unit wire & ground & the gauge should read about 1/2 that checks the wiring & dash gauge hope this helps

 

Pull the sender out, and operate it while looking at the gauge. Move the arm up and down.

In working with fibergl*** cars, I just got used to running two wires to the sender.

Grounds are always a problem on rust buckets. Those cheby's have been cut-up and smashed-up so much, that most of them are tempermental in the wiring department.

 

Thanks guys,lots of good help here.I will mess with it tommorow after i get off work in the day light.Im suspecting a ground problem .Might possibly be the float is bent wrong.I didnt install the tank or the sender ,so who knows .Thanks again for the help .Its odd though ,because everything else on the car works perfect,highbeams,cig lighter,interior lights ,speedo ,factory temp gauge ,etc...