68 fuel gauge

[AzDon]

I just went through this a couple of months ago...... Here's what you do to isolate the sender as the problem....
That brown wire has a connector that can be unplugged.......
Disconnected puts the needle at one end of the gauge and grounding the wire puts the needle at the other end (I've forgotten which function is which end of the gauge)
If this test produces these results then the problem is either the sender itself, or the last piece of brown wire going to it..... The problem on mine was that the float had a hole in it and sank ($6 from LMC)
As for the hole in the floor, I would NOT use a circular saw!! The PO of my burb had used a circular saw and the hole looked like crap because he had run past the corners some and then resorted to chiseling to cut all the way to the corners because the circular blade wouldnt go all the way to the corners underneath without WAY overrunning the corners on top.... Obviously you cant use a sawzall or sabre saw because youd damage stuff underneath....
The correct tool for the job is a router with a quarter inch straight blade and a proper frame (fence) fastened around it. This solves both the depth issue and the corner issue. Just drill a hole where you want to start the cut, set the depth, and away you go!
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Good Luck!