I would like to think I'd have verified that before I cut it, but there's a real possibility I wouldn't have after all. Anyway, you should be able to either open the cigarette lighter end and see which terminals the wires are soldered to. The center one *should* be the positive, and the ones on the side *should* be negative, since most systems are negative ground. If you have an ohm meter, you should be able to just check continuity between one of the wires and one of the terminals on the cigarette lighter without opening the adapter.