I will try to use the other wire (which I believe is white) that comes off the source coil. Or I can try swapping the lighting coil wire to the daytime circuit and I'll see if that fixes it. in the meantime, I ordered a new battery. I just spent all afternoon checking the resistance of every wire...

Or maybe give it a rev on AC volts on each wire individualt to see how high they go unloaded tested at similar safe high revs.

The charging system won't fix a bad battery.  It's like a short...  huge power draw...  on the charging system.

Yeah true 'that', as Mark says. Maybe leave alone untill your new battery arrives. My "07 Passat TDI battery is on its last legs & battery is close to $400 here for a high CCA type that fits. Not looking forward to that lol.

As Mark and RT said without a new battery in the circuit nothing will work properly these are super basic electrics , the battery charging circuit relies on not supplying all the connected items as well as charging the battery at the same time. It presumes you aren't operating the battery fed items all the time , if you use the brake light horn and indicators all at once the battery will flatten even with the engine running , a healthy battery is essential to give power when a lot is needed and it kind of acts as a regulator pulling down the voltage when it tries to go high , you need a decent battery and really clean connections 6v is not a lot its easily lost through bad scruffy connections .....

Thanks for the advice everyone. I’ll be waiting for the new battery. In the meantime, I’ll be pissing off all the neighbors riding around the neighborhood until my brake lights work again!!