Thanks for the reply. :)
The 64 is different.
The 65 is also the same as the 68 and I have one of those.
Used that and a new sending unit to test. (out, on the bench)
The 68 gauge runs up and down with the float, the 64 just pegs full, and if you either move the float to empty, it has a very slight movement (almost imperceptible) but stays pegged at full.
If I remove power, lower the float, and then put power, it drives full again.
I suspect one of the coils is bad, but I don't know where to get the winding or what size wire.
If I cannot find one, I will send it off to someone who repairs them. (anyone have a source?)
I did find a gauge that is listed as "NOS", but it is obvious that it was installed as the needle is faded on the front, and normal orange on the side, and the edge of the gage looks like someone pried it out of the housing rather than turning it.
So, I would rather not spend the money on something that "iffy".