Last winter we lost all 12V coach power in our 2006 Beaver Patriot. Everything seems scrambled -- the slide pump would try to run when lights were turned on and lights were all dim. There was only about 9 Volts between the ground buss and the 12 Volt buss. It turned out the grounding system for the Multiplex wiring system had failed. Installing a new ground wire between a lug bolt on the chassis and the ground buss in the Multiplex wiring closet got things working until the open ground conductor could be found and fixed.
The problem cause deserves a heads up for this group. Monaco installed a ground buss bar in the engine compartment, near the engine heater plug. It was an aluminum bar attached to the steel chassis using plated self tapping screws. The mounting screws provided the ground connection for the entire coach. When it got wet, all those dissimilar metals started corroding. The force of the corrosion broke the heads off all three screws attaching the bar to the chassis. An open circuit resulted causing no coach power.
If you have problems with 12V coach power, this should be the first place to check. I repaired it by installing a new grould lug and ran a #6 wire to the ground buss. Hopefully the ground wire will carry the current, not the mounting screws.
