google Allis Chalmers model C wiring diagram. Diagrams are in the operator manual, not usually in the service manual. The C was positive ground, so should have one heavy (neg) cable to starter terminal. Power to system also comes off of that terminal with a smaller wire.
Pg 4 here has an IB diagram, same as C, but for voltage regulator system.
Pg 3 here has original diagram under "WD45 generator".