Not sure if yours is the same or not but on my 68 C-10 the dash unit has a printed circit board.
all wires go to a connector for the board not to each individual idiot light. I grounded the hot side of the guage and got a full sweep to empty the default on the guage is full so must be a bad tank float unit. New one should be here today from American Classic. Will let you know the results.
