I just bought a new car with a sony cdx-f7700 CD player installed where is the aux audio input slot located on it?

There are six RCA-style plugs on back of this unit. As you're looking at the back of it, the AUX input is the lower left (red) jack. Be advised that if you're running something like an external CD player (if anyone still does), it will be plugged in there. You can't have both, so you'll have to decide which you want more.