Need Help With Stereo Install

[1000 Mile Stare]

Hello everyone,I recently purchased a 2010 Vibe and I am getting a bit confused installing a new stereo. Do all vibes have amps or just the ones with monsoon systems? My vibe is pretty base (locks and windows are manual) but it has onstar on the rear view and has an extra antenna which I am assuming is for XM. This is where it gets weird. When I removed the existing aftermarket stereo, I found that it wasn't even hooked up. In the dash, there are two stock looking harnesses, (female plugs... not sure about the terminology) , neither of which have wire colors that match the sticky on this forum. What looks like an antenna wire does not have a plug that matches either my new stereo, or the old one. I think I can use a multimeter to figure out the wires, but if anyone could help me determine whether or not this thing has an amp, it would be most helpful. I did feel a plastic box with wires under the passenger seat where the sticky says the amp should be. Could it be something else? Thanks for reading.