Re: 12V Connectors
Easiest bet is probably to find Radio Shack and get a "pack connector" or "Molex" connector that has two pins and is polarity keyed so it can't go together reversed, those are the most common way to do it.
Or instead of butt connectors, put in 1/4" "qd" connectors, the one is a tongue the other is a female socket for it. On the same crimp connector rack in the stores. When I'm doing connectors for 2-wire polarized circuits, I'll put a female on the positive supply side, making it harder to short out if dropped, and a male on the negative supply side, so again the two wires can't be plugged in "backwards".