I just bought a BEC on-line because I bought a used Heli that needed one, but the thing has no documentation whatsoever and I have never used one before. My question is this: the pair of red/black in are obviously the input power, but on the other side there are TWO sets of 3 wires out - one with a male 3-pin connector, obviously to provide power thru the receiver, but why is the female 3 wire connector there? Thanks.

What is the make and model of your BEC? Where did you order it from?

I figured it out - it's a switch.

The instructions are pretty clear in the pdf file.