It's also where the power comes from to power the rotor. Think about it if subjectively if you can.You jack a NUT, you would know if your regulator had a short to ground I think.
Brown wire is going to throw off the charging voltage. That wire is the wire the regulator uses to sense the battery voltage, so it knows how much power to send out through the green wire to control the magnetic field created in the rotor. If you add connections in line to it, the regulator will think the battery voltage is lower than it actually is!!!! Jaxk a nut!