My 01 non Bose system with factory rear sub..Sound terrible all speakers playing poor and no sub sound..if I replace the head unit can I buy a harness to use the existing wires? Is it possible my amp is bad behind the glove box?What can anyone recommend..very new to ohms and volts required?

 

You can get a number of harnesses that will allow you to use the factory wiring. In most cases you use these to use door chime, steering control, Onstar, the factory amp and speakers.

Pac audio has a number of items that may interest you.
Pac-Audio.com Product Search | iPod Integration for your car and More by Pac-Audio - Connecting you to the future

You may want to visit the crutchfield.com website and look at some of the options available and then call one of their sales staff to put together a spec for your Tahoe.

Unfortunately, due to the age of your truck, you should review the existing speak wire, as some of it may need to be replaced.

The amp should be located under the center console.

Good luck with your audio upgrade.