Q; do I need a resistor for the tail light and another for the brake, or can I put one resistor on the ground wire?I confirmed on my 2007 F800 ST that a 100 ohm resistor 2W or larger solves the LAMP errors. Then any LED bulb with the correct base will work for tail brake or turn.
You need a resistor for each bulb in parallel.
Also; I'm in Milw too; near Mayfair.