Garmin Handheld Question

I have bought a Garmin Etrex venture handheld GPS. I am trying to hook up the external power(12v). I am having problems with the handheld reconizing the external power. How or where is the setting to tell the handheld to use the external power?? The manual that it comes with is not much help..

On mine it tells you its hooked up. Where the battery life bar is, instead of being bars like a cell phone its a small receptacle plug instead.