I've installed one end of the extension to my aileron servo, the opposite end of the extension is inserted into my servo tester. A battery is powering the tester. I wiggle each wire terminal to make sure of good positive connection. This servo tester can center your servo. or it can be set to manually control the servo by the black knob on the tester. This servo tester will also "burn-in" your servos by continuously cycling the servo from one end point to the other indefinitely.