The setup comes with an inline fuse. No relay. The brown wire is for an electric squirt system but you have to supply the reservoir with 12-volt motor.
Ray is right about knob placement. When the knob is pushed in, the brown squirt wire is energized. If you want to add a relay, you could make the brown wire energize a relay coil. That way, the squirt motor can draw power from relay contacts, not the wiper circuit.
I'm using the interval setup and I love it. - Dave