So for anybody else who has this question years from now, here is the answer, thanks to Mike Bickford at Campbell’s Boatyard in Oxford, MD. The switch in the lower position allows the furling motor to work in or out. In the upper position, the switch locks the motor to prevent the sail from unfurling or furling (handy with a reef set). The middle position has no effect and is the same as the lower position, but you run the risk of the switch sliding up into the locked position accidentally. To engage the switch, you have to bump the furling motor a tad one way or the other.