4 WINDS COACH BATTERY CHARGE

I don't have a 07, mines a 2000. Inside the rv electrical box there are solenoids, One is activated by the aux start button on the dash. This connects the batteries together and is also energized when the key is on so the alternator voltage gets to the chassis battery, that solenoid also has a fuse for the coil. Press the aux start button with the engine off and see if the solenoid clicks, if it does, the fuse is good. With the engine running, check across the solenoids big terminals, If you read voltage and the solenoid is energized, the contacts may be bad.

This is mine, I'm pointing to the relay. the fuse for it is to the left center. It might be nothing like yours, under the hood.