[21sH2]

It depends on the brand of stereo you install. Most brands will have a metra harness that will work in correlation with another metra harness specific for the hummer. I add my vehicle on the circuitcity website and hit audio accessories, it will give you the specific metra model you will need for the hummer. As for the unit harness, like i said it depends on the brand. You can usually find one that will work with your new unit from metra as well and then it will all be plug and play. each harness usually costs 15-20 bucks. Replacing factory amp will bypass bose if you have it.