[prairieschooner]

I was going to hold off until I finished but here is what I know so far about the older systems after talking to a representative from Jacobs.
These older Jacobs Brakes usually did not have a Control Box. We have a Micro Switch that is energized by a piston type unit that attaches to the Governor. This Switch is energized by a "No Fuel" situation. It looks like this.
   
Now the System changes to Hydraulic where the Solenoids (1 each per side) inside the Valve Covers are energized. In our case it appears to be an Electrical issue so I may not need to pull the Valve Covers.

I didn't get a signal out of the Micro Switch when I checked with the my Digital Volt Meter. Wasn't sure if it wasn't fast enough but the Brake still didn't work when we came home, if I was any further from home I would have repaired it there. I have ordered the new Switch and will install it later, I just didn't want to start removing engine parts while at a State Park and Dry-Camping.