Hey i was trying to hook up a speaker box in my truck so i was going to splice the speaker wires when i noticed in the middle of speaker wires is a third plug as if it was supposed to be plugged into a third speaker....but when i tried to use that wire on my speaker it didnt work....

anyone know what that wire is for??????

it comes from front of car and one wire goes to speaker 1 and 2nd wire goes to speaker 2(duh) but the third one is just in the middle and not plugged in....what is it?????