cut-off switch question

I have a 48V brushless Skyhawk electric bicycle kit. It has a cut-off switch built into the hand brake lever. I can't use this hand brake so I was wondering if someone could explain how the cut-off switch works so I could fabricate one myself. I can't identify the model or make of my controller. The cut-off switch has three wires black, green and red they plug into controller wires black, blue, red respectively. I'm not that knowledgeable about electronics; I would have thought the cut-off switch was just a circuit breaker but if this is the case I don't know why there are three wires.