Someone-Sometimes-Somewhere-had told me how to test the fuel gauge in the 68 to see if it is the sending unit or the gauge itself, causing the gauge to be pegged past full. 

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Disconnecting the power wire from the sending unit should peg the gauge to Full. Grounding the signal wire will peg it to Empty. The signal wire is normally Tan, or a pinkish-tan color...the wire color changes with age. It would be the wire going to the larger terminal, usually a round one, towards the center of the sending unit. The ground wire is connected to the outer edge area of the sender.
If you ground the main(signal) wire, and the gauge stays pegged at Full, then there is a break(open) in the wire from the tank to the gauge cluster somewhere.
At the gauge, there should be a pink, and a tan wire. The tan wire is the one from the sending unit, and the pink is power for the gauge. With the cluster out, but connected, you should be able to ground the tan wire at the gauge, and it should go to Empty. If it does not, then either the gauge is defective, OR there is no power going to the gauge on the pink wire.
hth


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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Okay I disconnected the power wire from the sending unit, (the center connection.) I used a power strobe and grounded the wire. The gauge went to empty. Then I plugged this back in and took off the ground from the outer ring and grounded this connection. Not the wire but the connection at the ring.  The gauge went to near the full mark. I have approximately 3/4 fuel in the tank. So it did not register correctly, but at least it wasn't pegged past full. I removed the gas lid and maneuvered the sending unit and this did not change the fuel gauge.

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So you say you can move the float on the sender, but it doesn't move the gauge?
You prolly have a sender that is just too corroded, or the tiny wires on the sender are damaged.
I don't know about you, but I would mush rather mess with the sender unit than fart around with the gauge cluster.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I agree, I think I will order a new sending unit since I have already gone through the gauges several months ago and put in a new fuel gauge. Think I will wait until it cools off first. 103 is too hot to work in and then in my garage it is 108 at least.  

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