@jhetzki21i got the same problem sir on my motorcycle when i cut the "yellow wire" the thing is when you cut your yellow wire. the charging current is not stable and yes it exceeds to 15Volts. what i did was i bought a diode here on one of our local electronic store . i don't know what diode it is but what i said to the saleslady was "pabili po ng diode yung pang motor" it cost me P15.00 only. so after i put the diode on my yellow wire (remember that the diode has polarity) after that i tested my charging while revving realllllly high and i only got 12-13volts. idle is 11-12 volts. i tested it with my digital multimeter.
Sir you cut the yellow wire for fast charging, where did you put the diode on the yellow wire that you've cut?? and where does the end point of the diode connected to?? I'm just confused..