You are correct, but the reason I bring up the ground wire is this:
If the IVR is not gronded the contacts in the IVR wont open or pulse. It will send unregulated 12v to the gauges and senders .
IF you had the ride in the garage cold and not running with a full tank of gas, turn the ignition on, you will certainly take out the fuel gauge sender or gauge. Dont ask me how I know.
Lets just say I replaced the most expensive dash bulb ever.

 

My '67 has a similar issue. Would this fix also work for '67s, or is the wiring different?

 

 

Dose it matter witch wire goes were on the back of the fuel gauge and the same for the temp gauge?

 

When you turn the car on, does the guage move even a little?

If it moves even a little up to the E then most likely it is your sender. If you've tried all the ground techniques then it might be the sender. If someone replaced it recently then it's probably one of those plastic bowls in your fuel tank that can easily corrode. I went through two before a friend of mine showed me a brass float.

James

 

Thanks James for the best answer. The quickest way to figure it out is to pull the wire off of the fuel tank unit the gauge should go below E (empty). Ground the wire at the tank and it should go all the way past F (full). if it doesn't do either it's in the gauge or the IVR circuits (including the instrument panel ground wire that attaches to the IVR screw)