[wild man]

1. I don't know off-hand, but if it was me, I would test all of the wires (but not the speaker wires, which you can tell by the fact that they are "siamesed" pairs that are the same color, with one having black, or white, stripes on it) with with a volt-ohm meter (VOM) or digital multi-meter (DMM) - I think wal-mart has one for less than 10 bucks or so. Use the 20 volt DC setting, with the common (black) lead on reliable ground point, and look for a wire that reads 12-14 volts when the key is NOT in the ignition - that is where the memory power (yellow) is connected. Blue is a little trickier because you can't simply "test for voltage" on that wire. But if you do not have a power antenna or "external" amp, then you don't need to worry about it, other than making sure that the blue wire coming out of the radio can never come in contact with anything that is a ground, or you risk frying the power (on/off) switch on the radio.

2. Yes; and no, not necessarily.

3. You always have an amp, as that is what drives the speakers. But it can be internal (most radios have this) or external, or both. A typical "both" setup uses the internal amp to drive the front speakers, and an external one to drive the rears. An amp is being overdriven when you turn it up to the point of starting to hear distortion in any aspect of the sound. Continuous operation beyond this level is usually what damages speakers!