1972 Plymouth Valiant 4 door Auto Slant 6

Currently chasing a fuel gauge issue. Have no power out to Coolant temp sensor, no power to back of the gauge cluster. new circuit board, new sending unit in tank, new 12v to 6v regulator, and just replaced fuse 3A and i need to test for voltage but not sure where to go from there if I don't get V output from that back of gauge regulator.