Fuel gauge issue

[dave`12]

A while back I replaced the sender, and all was working well. Other day, the battery died. After jumping, the fuel gauge read 1/4 tank (it was over 3/4).

Shut it off, on the next restart, the gauge read empty and has stayed there.

I unhooked the wire to the sender, gauge went past full (way past).
Unhooked tan wire at fuse box, same thing.

Checked voltage at the box where the tan wire goes, 7.8. Test light lights, but dim. Is this supposed to be less than 12?

Ran a new wire from fuse box to sender, and the same thing happened, so I think that wire is ok.

All fuses seem ok (does anyone know which fuse controls this? I can't read anything on the old box.

So what is the next test?

thanx