overcharging problem on Chrysler 318

Hello everyone especially those with electrical expertise:
I have a voltage problem on a Chrysler 318 in a 1977 Tucker Sno Cat. The volt meter shorted out when the wire attached became loose. I have replaced the alternator, voltage regulator, and volt meter.
When the engine is idling, the volt meter registers about 14 volts. when the rpm are increase the volt meter is pinned.
What is strange about the wiring is that two of the wires leading to the volt meter must be connected together; otherwise, the engine can't be started.
The wire connected to the negative side appears to be a hot wire. When take off the volt meter and tested it registers high voltage. But when removed from the volt meter, the meter registers no voltage.
So, why won't the engine start without the two wires being connected together? And, why is there a hot wire going to the ground on the volt meter? Additionally, why won't the volt meter register without the hot wire being attached.
I have tried to trace the wires in question, but the wires are bundled underneath the dash and the same on the other side of the firewall. At one point in time, there must have been a lot of electronics on board because there appears to be a lot of excess wiring.
Any suggestions, advice, or comments would be greatly appreciated.
TIA
Jim