What is the second plug for on the back of the stereo? Its a small blue square. I want to upgrade to a new deck, and i found the wiring adaptors, but they only have the one large plug. Is this small plug the one running the tweeters or something?

 

That is for the mid range speakers located by the dome light. I hooked them up with my front door speakers. They sound great..

 

you will need a resistor if you plan to hook them into the front speaker channels... otherwise they will be insanely loud right by your ears...