The following article is a result of numerous EVC's coming through our shop with the same symptoms.
All Eurovan Winnebago campers (EVCs) have two batteries, the main battery under the hood for starting the engine, and a second deep cycle battery in the rear right compartment that runs the camper stuff. This second battery was installed by Winnebago when they converted the Eurovan to a camper.
Above the main battery is a silver cylinder with three wires going to it. This is the solenoid responsible for charging the second battery when the engine is running, and for isolating the two batteries from each other when the engine is shut off. The two wires going in and out of the large posts on either side of the solenoid go to the positive posts of both batteries, one to each battery. The third wire coming off the small post of the solenoid is the "trigger" wire. Whenever the ignition switch is turned to the "ON" position, the trigger wire sends a signal to the solenoid to come "ON", which bridges the tow battery's positive posts so the alternator can now charge both batteries while the engine is running. It is a common occurrence that when the fuse box of an EVC has to be dropped for any reason, the trigger wire comes unplugged from the fuse box. This wire is usually purple on 1997-99 models, and on 2000-2003 models it is usually yellow. Whatever the color, it is only about a foot long and it is easy to trace back to the solenoid. Attached are some photos of the solenoid, and the back of the early and late fuse boxes showing where to hook the wire back up.