After Market Fuel Gauge 1966 Dart?

There is a little strap, about 6 inches long, that goes from the fuel tank sending unit, over the rubber hose and clamps onto the fuel line. That would be your ground.
I haven't replaced the fuel gauge yet. It is on my list of things to do/get. I have to rebuild the steering coupler, replace the pinion seal, reinstall my engine, trans, clutch assembly, radiator, headers and new u-joints. Then it's gauges. Oh, and also the fuel filler tube restrictor.
Lots of things to keep me busy.