If its like our 93 Bounder, the relay is front to the left in a large box. Mine had a plexiglass cover. There are two large relays, one for the chassis and one for the house.
Try this: first hit the boost button and see if you get anything. Hold the boost button and try to start the engine.
If that does not work, take the cover off and tap the relay, then hit the button for the chassis battery.
If that doesn't work, you should be able to disconnect the wires from both side of the relay and connect them, if there are no other problems you should get juice.
Almost forgot, check all your fuses first, inside and out.
2001 Itasca Horizon 36LD Cat
Retired Air Force, One lovely Angel
, 2 Cats and three birds.