Adam,
I'm not sure how your coach is wired, but I don't think the problem is a relay, as the switch normally energizes a relay. I suspect either a blown fuse or bad circuit breaker. Check the diagram for your electrical bay. If it's wired like the 2000-2003 Marquis, it probably has a circuit breaker for slide power and a couple of terminal block connections for slide switch power and slide switch out. The side switch power should be the switch input and slide out, the signal to drive the pump motor. The circuit breaker is a thermal reset type that will open when it get hot and reset when it cools down. If you've got 12v on the buss bar, you should also have 12v on the circuit breaker terminal. Oh, and be sure the ignition is off. If it is on the slide circuit is disabled.
Steve