OK guys, I have seen many people ask questions, and I was too.
I have got some answers.
the rear door speakers are 6.5", the wire colors are:
Left side (-) tan (+) white
Right side (-) red (+) tan
I have a 2000 Tahoe Z71 old body ( same look as 95-99), the rear door speakers in my truck are factory amplified. only these two speakers though.
The amp in my truck was located under the dash, above the gas pedal, just behind the horizontal knee bolster bar/pipe. It is silver in color and about the size of a stick of deodorant (squared corners of course) (only common item with same size I could think of)
The wire harness going into the amp has 10 wires. Orange: 12v+, Black: ground, Red: R- output, 2 Tans: L-/R+ outputs, White: L+ output, Brown: L+ input, Yellow: L- input, Dark Blue: R+ input, Light Blue: R- input.
I'm not sure if the speaker inputs to the amp com directly from the stereo, from the rear roof speakers, or from a splice somewhere.
Now, If your truck has a custom stereo, and your rear door speakers are not working, it is most likely that the installer neglected to hook up the amp. This can be done by connecting the pink antenna wire from the factory harness to the blue remote or power antenna output of your custom deck. OR, you can just run a direct line from a constant 12v+ to your orange wire on your amp, but unless you put a switch on this, you will suffer battery drain as it will constantly be on.
If you have the factory deck, and your rear door speakers are not working, don't be dumb like me and start ripping apart the whole dash and such looking for the problem. I spent 6 hours today searching for the problem, before I finally called a Chevy dealership and had them print me out the wiring diagrams. COME TO FIND OUT: it was just a fuse. The amp on my truck draws its power from the cigar lighter circuit/fuse. Which in my truck, the fuse was blown. So after 6 hours of multimeter/voltmeter work, all I had to do was replace the fuse. At least I got to know my truck!
1: pic of the wiring harness
2: pic of the amp relative to the gas pedal.(wires on top are the amp harness)
3: pic of amp from below dash (note: the heat sink that looks like an amp on top of pic, is not the amp)
4: speaker wiring diagram
5: amp power diagram
any other questions, or need bigger copies of photos, let me know.