[RichardJ]

This image may look a little messy, but it shows both type of switch. This isn't a combination valve, just the distribution block and switch, but shows the two separate flow paths indicated by the orange and yellow wires.

The threaded hex piece in the middle of the image slips over the nylon insulated pin next to it. The pin makes contact with the inside shoulders of the brass piston, when the unequal fluid pressure pushes it either left or right. The piston has O-rings, so the electrical path to ground is actually through the springs. The switch contacts are the pin and the piston.

In the lower part of the photo is the type of switch with a spring loaded pin. This is a conventional type switch that is grounded through the body of the switch. For this type switch, the brass piston will have tapered shoulders to help push the pin into the body of the switch.