Squat Switch Explained

"The squat switch itself is nothing more than circuitry. When you are on the ground and the gear is locked down, the squat switch circuit, which is on one of the mains, is separated or "open." When you lift off the ground, the gear falls to full down position, thus closing or "completing" the circuit of the switch and allowing the electric current to activate your hydraulic pump. This is the reason your gear won't come up when you are on the ground and the lever is up...in this case, since you can't activate the pump because the circuit is open, your lever is useless, kind of like turning the power to your tv on with it unplugged."  - Goldmember, Jul 3, 2008 Jetcareers.com