rear speakers not working

I have a 2000 tahoe limited i installed an alpine stereo and now the rear door speakers dont work also the rear speakers above the cargo area dont work either. can anyone help out. i used an installation plug that i got from best buy they said it was the right one but the stock stereo has two plugs and i only got one from best buy. any help would be appreciated

Nice installation guide for a 2007+ tahoe...

There is a remote amp wire that has to be connected to operate the factory amp that powers those rear speakers. I think the wire is blue like the remote wire for powering amps. Try that.