[JRTJH]

It's not a "switch" but two valves that you'll be looking for. One is under the sink, above the unheated space and the other is behind the refrigerator, also inside the heated space. They are 1/4 turn valves, should be in the blue PEX line that goes to the cold water faucet on the galley sink.

The purpose of having two valves (not switches) is to turn the water off before it flows into the "below the slide plumbing". That way, you won't damage your ice maker line during winter's freezing temperatures. The valve behind the refrigerator is there so anything that might melt in the ice maker or any water that's in the line behind the refrigerator won't flow back down to the exposed plumbing.

There is a diagram in the Keystone Owner's Manual that depicts approximately where the valves are located, but each trailer can differ from that basic diagram, so you might find it somewhere "close by".... If you go under your trailer, you'll find the 1/2" PEX line that connects to a flexible line which enters the slide under the refrigerator. Follow that line toward the center of the trailer and you'll see a "low point drain" under the galley sink area. There may also be a 1/4 turn valve on that low point drain. Some have the third valve, some don't.