Originally Posted by SouthArk370Z

Yes. 1, 2, and 3 are the "music" signal wires. I do not know what level the signal is. If I have to guess, I'll say it's probably ~1V P-P (line level).

It's the "oval" connector at the sub unit.

I'd go ahead and kill the factory sub amp (break the amp on line or the B+ supply), but it probably won't hurt anything to let it idle.

You really ought to re-download the FSM or at least the AV section. You can find the whole thing in the Tech section of this site.