the amp turn on wire in a 2001 Yukon xl without Bose and WITH a factory subwoofer is located in the 9 pin connecter from the back of the radio and the color is pink. you need to run the remote wire from the aftermarket deck to the pink wire.
There is a big problem with using the amp factory amp as is in this setup because the amp has 2 functions: its a LPF and amp for the sub as well as a HPF crossover for the door speakers. I suggest you bypass the crossover portion and leave the amp portion. This is easily achievable if you follow these instructions:
http://www.savagehomeautomation.com/projects/bypass-factory-ampcrossover-in-2002-chevy-tahoe.html
I also had a factory subwoofer in very bad shape when I bought this truck but I fixed the speaker in about 15 mins using this kit:
https://www.simplyspeakers.com/panasonic-speaker-foam-edge-repair-kit-fsk-8-1.html
I hope these things help you as much as they helped me.
Enjoy!