The schematic pictured above shows all those blue wires connected together before the regulator. Did you find that connection where they are all soldered together? It has to be there somewhere. Where does the blue wire go from the regulator?
It has to have a power source. It comes from the ignition switch but before it goes the regulator it splits off and goes to the Alternator, ballast, and choke thermostat, You have to have that soldered splice in the harness somewhere or how would it reach all 4. You must not have looked very well or your harness has been changed around.
Testing You can take 2 wires from the voltage regulator blue wire. One to the battery and one to the alternator blue wire.. That should correct the charging for a test