1 quick (dumb) gauge question

If your '71 is like mine you will not have the round connector, but rather two flat connectors that push onto the pins at the back of the dash one on each side. The fuel and temp get their power/signal from being connected to the dash using nuts on the studs. The signal/power/ground is all provided by the printed circuit board. The signal in to them is carried to the dash by the flat connector of wires on that side. Hope that helps.
Cheers