How do you test the solenoid in a Ford E450 bus that controls power between the chassis battery & house batt?

I have a Ford E450 and I understand there is a solenoid on the firewall that controls voltage between the chassis battery and the coach battery. How do I test it? |||Energize the solenoid with one of the batteries disconnected and then test for power on the other terminal. There is a small 12 volt light that can be used to test the unit for 12 volt power. I'm not familiar with the wiring for that system, but I would disconnect the house battery side and insulate the wire while I do the work. While I am in there, I would clean and tighten all of the connections on the solenoid and the batteries and also the alternator and the grounds. |||My experience has shown that the solenoid is installed by the coach builder, not from Ford. The location and wiring method will vary from one manufacturer to another. In my last Ford powered Winnebago, the solenoid was in the coach battery compartment,curb side. However, most solenoids can be tested the same way. There should be two larger gauge cables and one or two smaller wires. One large cable leads to the coach battery positive. The other goes to the alternator output or chassis battery positive. This isolates the two batteries when the engine is off. The smaller wire/s are the control circuit. One will light a grounded test light when the ignition is on and/or engine running. The other small wire, if present, will be a ground. Some solenoids self ground thru the mounting bracket, not needing a seperate ground.