Gray water dump on 2002 King of the Road

As a 'mergency thing, it is possible I suppose to pull the house battery, drag it around to the side and hot wire a temporary jump to the dump valve. That would let you at least dump a currently full tank and give you time to track down the problem.

My guess is that you'll find a wire somewhere that passes through some bulkhead and was not grommeted properly, and abraded until broken. But that's just a guess.