Casey,

I see your profile indicates a '58 rig which I'm not real familiar with. A 'typical' setup for many early rigs used a ammeter in the dash. The output of the charging system was on one side of the ammeter while the other side was connected to the battery via a large terminal on the starter.

This results in power to the cab continuously which is common. Power for any accessory, the ignition or any other item would be on the switched side of the ignition switch which would be powered by the charging system side of the ammeter....hot all the time (from the battery).

The ignition switch is the 'master' that is always powered and passes it along to ignition and accessories only when turned ON!

Your truck may make the connection between charging system and battery in the engine compartment. I believe how this was done in later years. Regardless of that, there will always be battery power inside the cab which is controlled by the ignition switch...the battery side of that switch will be hot all the time.

Stuart