[mr0077]

The diagram from PGMR posted by J Persons essentially uses the firewall solenoid to energize the starter solenoid. Why not just run direct from the battery to the starter and from the ignition switch to the solenoid trigger terminal, eliminating the firewall solenoid and cleaning up the wiring?

If you want to use the firewall solenoid, it would be more conventional run the B+ cable to the firewall solenoid, big cable to the starter solenoid, and a short jumper on the starter solenoid. Wired that way, the ignition switch energizes the firewall solenoid, sending B+ to the starter. That energizes the starter solenoid, which completes the circuit to the motor at the same time the starter gear engages the flywheel. Don't see any downside to it.

Just my nickel's worth...