04+ RSVR R/R Upgrade to FH020AA Black Wire

I noticed there is a gap of information for 04+ RSVR Factory bikes so I'm trying to post up some issues and conclusions to help others. I installed a new stator today and have the new Mosfet FH020AA R/R almost wired up. Its showing 14.26 volts at idle which is awesome. My issue is the stock R/R has 2 green and 2 red/white wires and a small black wire in the middle. Green wires are ground and red/white are positive. The black wire is 0 volts with key off and 14 volts with key on. They say the black wire is no longer needed but would be nice if this could be used as an auxiliary wire to run a radar detector? Does anyone know what the main function of this wire is in the stock wire harness? Thanks.

The Black wire is a called a "tap".

On the oem reg it feeds the battery voltage back to the regulator to tell the reg the state of the battery charge.

Perfect. Thank you! I hooked up the Mosfet FH020AA without the black wire and tied the old harness into the ground and battery line. Everything is peachy. After starting her I had an issue with the idle. It would not idle low enough, just hangs at 2000-1500. Turns out the person who did the EVO air box mod put smaller diameter hoses inside the hoses that run to the IACV. I did a little more digging and found the hose from the rear throttle body to the vacuum pump split. I removed the smaller hoses from the main tubes and did a throttle body sync with a sync tool. I put some die electric grease in the plug to the stepper motor and tried again. Huge difference. I also found an idle screw. I came across an article somewhere that said 04+ RSVR's don't have idle screws, they are regulated by the ECU and IACV. I removed the idle screw and it idles perfect at 1250. The power difference between the old bike and now is outstanding. Before the new stator, R/R upgrade, and throttle sync, the bike had bad backfiring and a heavy fuel smell after riding. The backfire and fuel smell is gone. I hope this info can help others.