Reply to "Tach and fuel guage stopped working......?"

The tach may be toast. There are glass resistors in a small circuit board inside, and I've found at least two tachs with cracked components, opening the circuit. If you can borrow a known-good tach, try it; if it works, that's the problem. A good speedo repair shop might be able to fix a bad tach, or you may find a used one affordable. Pantera and Mangusta tachs are identical.

Regarding the fuel sender, there is a curved wound-wire potentiometer as part of the sender inside the tank. The wire is very thin and sometimes breaks as the contactor rubs across the turns. The late sender is still available at the vendors, is not outrageously expensive and fits your early car's tank perfectly. The late assembly includes a fuel-out line built-in, fixing the two main tank problems in the early car: rust pinholes in the welded tank line that does not allow a full tank to be drawn into the engine, and a plugged and inaccessible filter-screen on the end of the welded line inside.
The simplest way to replace the sender is to first remove the left rear quarter window which is only held in place by friction of the rubber gasket to the body. A flat blade screwdriver can be used to carefully pry the whole window and chrome frame loose. On a few cars, the left 'gill' overhangs the window frame and must be removed before the window assembly can be removed. And sometimes, repaint overspray glues the edge in where imperfect masking was done.
Next, remove the engine screen cover and the left solid engine cover. This exposes the fuel tank top and sender wires. Mark the wires and disconnect.
Unscrew the ring of screws holding the old sender in, and lift it up and out the opening left when you removed the window.
THe new sender goes in reverse of the removal. I suggest plugging the old line and transfer the fuel line to the new sender fuel-out pipe. This all sounds complicated, but the entire operation is a matter of maybe 30 minutes, once you've done it a few times. Many of us remove the glass from the chrome frame and only replace the frame. This allows easier fuel tank/sender/wiring trouble-shooting in the future, and it's much easier to clean the big vertical rear window. Having the glass in place does nothing for or against the aerodynamics of the Pantera.