I don't have any info wiring it up like David suggested, but using this kit from Warn, it will cut off all power going from the battery to the winch.
<img src="http://www.pnw4runners.net/tando/power_interrupt.jpg" alt="" /> All I do is flip the switch in my cab, and it either supplies juice to the huge wire going to the winches solenoid pack, or it cuts it off entirely.

It's all controlled from this little solenoid, much like a battery isolator.

I forget what I paid for it, but it was not much.
Very easy to hook up. It wires up just like wiring up a Hella driving lamp with a relay, only the unit itself is the relay.
Corey