Just bought a sundowner LQ trailer. It has a tank with a spigot under the mangers for the horse water.

How in the heck do these work? I drove a long way for this trailer and this was the one thing I forgot to ask about.

I have the same type set up and main power has to be on inside the trailer, then mine has another rocker switch inside the manger by the little water pump.  With the main power on, I just flip the rocker switch then turn on the faucet.

Does yours have a pump mounted above the tank????  If so, follow the wires and it will be hooked to a switch.

Okay I don't see where the pump for it is, there is a rocker switch for it. So turn all the power on inside then turn on the rocker and it should work.

I shall go try that, Thank you!