[mr0077]

Either circuit will work, but I agree with Ernie, the diagram Fox had is not "typical", As said before, the firewall solenoid was used on Ford starters that did not have a starter solenoid. So if your starter has a solenoid on it, and IF you want to use the firewall-mounted solenoid (not necessary except maybe for looks or safety?), the "typical" way to wire it, described by Ernie and Rick, uses the firewall solenoid to provide battery voltage to the starter motor only when the key is in the start position. This system also needs a wire to trigger the starter-mounted solenoid. I have a jumper wire from the big terminal on my starter solenoid to the blade terminal. Both terminals then become hot when the firewall solenoid is triggered with the ignition switch, so when I turn the key to start, the firewall solenoid energizes, running voltage to the big terminal of the starter solenoid AND the blade terminal of the starter solenoid, causing the starter to spin. You could also run a parallel wire from the key or switched side of the firewall solenoid directly to the blade terminal on the starter solenoid to trigger the starter solenoid.
The diagram Fox has uses the firewall solenoid to trigger the starter solenoid, with the starter motor power uninterrupted, and direct wired from the battery.
Whew! That's difficult to put in words...hope the above makes some sense!