[Chester Stone]

Todd, my coach has two devices in the engine electrical compartment that relate to your issue. There is a merge solenoid that is activated by a switch on the dash to merge the house and chassis batteries. Since you mentioned that the alternator is not charging the house batteries, I would suspect the other device frequently called an isolator. Its function is to automatically allocate alternator output to the battery bank that needs it. It is often blue, has large heat sink fins, and three large battery cables attached. Perhaps another Guru can tell you how to check it out.