To add on to txbest, you'll have to take the rug away from the side to get at it. Also, here are the color codes for the wires. Yes, believe it or not. The factory sub has dual coils. The A7, A8, A9 and A10. Are the pins they are located in on the connection harness. It's Connector C3 and it should be LT blue color connector.
The amp in my 03 was under the rear deck cover, mounted on top inside the cab. The amp is not big enuf to push any subs worth mentioning, so I hope you werent getting your hopes up! I just ran an inverter and hooked up my own amp and then built a custom sub and hung it up where the stock sub sat, just from the bottom. It sounds so much better now and still doesn't take up any more room in the trunk than the stock woofer did.
Just replaced my 4 door speakers and the owner of Sight -n- Sound said if I add an an aftermarket woofer I would also need to replace my amp as the one in my 03 (not a Bose System) would not be strong enough