gas guage going crazy where to start the hunt??

My gas gauge has went crazy.
Sometimes it pegs way past full.
Sometimes it looks like it might be right then sometimes it will drop to full then back up and peg again way past full.

I know this is a common problem with these cars but it doesn't seem to match the problems most have with the fuel gauge.

This seems like some sort of short in the wiring to me.
I'm going to check the wiring in the morning.

Any other ideas on things to check?
I'm hoping it's not the sending unit as I can't find one local for my car.

Yeah I think I'm gona need that good luck.

Does anyone know if I can use a 85 carbed car fuel tank in my 89?

I've already deleted the EFI on this stang.
It's running a holley 670 with a red pump.
The reason I ask is I have a 85 tank sitting here with a working sending unit but I'm not sure if the sending unit will work with the 89 fuel gauge.

I'm hoping it's just a wire though.

Wheres the anti slosh located ?? Is it on the cluster?