Don't rule out bad Battery Cables. We've had recent cases where the molded factory terminal ends looked good but the connections were failed internally.
Also, you have a Starter Relay (called Solenoid by many) BEFORE your Starter Motor. Easy to find on a Class C, I don't know where it is on F-53, but it has a large battery cable TO it (from Battery Positive) and down to the Starter Motor on the opposite terminal. It has to be mounted to a grounded surface, and the small wire is what energizes the Relay from your Ignition Switch in Start position.
Jump the small terminal with the cable FROM the Battery, and the Relay should engage the Starter. That can be done with a light gauge wire. You can also jump the two Large terminals with a Booster Cable or a big pair of pliers. That too should cause the Starter to crank.
Finally, starter, too, has its own Solenoid. It's a different setup from GM where the wire from the Key goes to the Solenoid. In Ford, the Solenoid on the Starter cranks every time it sees power coming down from that Relay I mentioned.
A friend called me from out of state, Class A/F-53 wouldn't start. Battery was both Dead, and Bad. Wouldn't start with a new battery. Had to replace Starter. I'm beginning to draw the conclusion that trying to start a Ford with a weak Battery can damage the Starter. I think my friend also replaced the Relay...
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB