I actually have the same issue on my 78 F150 Custom 4x4 back here in Sweden, sending unit seems OK, fuel gauge "dead", needle does not move on ignition-on.

Saw that you provided two different part numbers (leaded / unleaded fuel) for the gauge (are the sending units different, too?), how do I determine which one I need on my truck?

I also have an issue with the ampere-meter, doesn't work at all, wiring seems to be OK....