The chances of finding a comprehensive wiring diagram are pretty slim, unfortunately.
If the wire to the slide is going to the motor for the slide mechanism itself (as opposed to some lights or whatever that happen to be in the slide), it might lead to the switch for the slide, or it might lead to a fuse/circuit breaker near the battery or in the DC electric panel (and other, low-current wires go to the switch). If you figure out who made the slide mechanism and its actuator, if it's not something Shasta engineered themselves, you might be able to find installation or maintenance information about that which would show typical wiring.