The power for the electronics inside would come from the receiver plug. The two other leads are likely just switch a positive or negative feed. If it's relay based you could try plugging the receiver lead in with some power to the receiver. If it's relay based you may be able to hear it clicking on and off when you operate the appropriate channel with your transmitter.
But it's probably transistor based, so you won't hear squat, which means you need the ohm meter as mentioned.