need help with 1973 z fuel gauge

[bahrtman]

My fuel gauge is not working properly. It fluctuates between 1/8 and empty continuously. I replaced the float switch but it didn't change at all. Any suggestions would be appreciated. I hope I don't need to replace the gauge!

[VStar650CL]

Ground the gauge signal wire where it enters the gauge, the needle should shoot to full. If not, the gauge is bad. If so, ground the other end of the signal wire at the tank. If the gauge shoots to full then the signal wire is good, otherwise it's open. If there's a separate sender ground wire, short between the signal wire and the ground wire. The gauge should again shoot to full, if so the ground wire is good. If that all checks out, the sender is shot.

[bahrtman]

Thanks for your help. That should give me my answer!