It sounds like your warning light is a different system. On the 2008s the ignition key goes to the idiot light directly, and then the ground for the light goes straight back to the "L" terminal on the alternator. I talked at length with AJ about the terminals, as I didn't want to screw it up. He says the "L" terminal is simply a line to the alternator power output, that goes through a resistor and to the terminal. If the alternator is not producing power, the L terminal acts like a ground, so the light lights up. Once the alt is producing power, then the feed from the ignition and the alternator "L" terminal are within a volt, so the light goes out, since there is not enough voltage difference. Then, if the alternator voltage regulator fails, the "L" terminal will be putting out well above the normal 13 volts, so there is once again enough differential to light the light for over-voltage.
It's super simple...but it only monitors 2 failure modes. It sounds like your unit uses a module to sense other failure modes too...like bad diodes etc. Just guessing. I do know AJ said in 2009 Monaco went to a more mainstream alternator, instead of the special made that mine is. AJ said the "W" terminal is an AC output...and my unit came with a cap on it. I would think you have a module that is using this AC to diagnose problems and then trigger the warning light?!?