I failed last week on city bike with a minarelli and ext ig ground tried forever and got nowhere.
1. have the right switches, normally closed?
2. the switches are not grounded to body? from switch terminals to ground.
3. Is the tail light grounded good?
wiring is pretty straight forward. from ground to one switch to the other switch and all the way back to the rear brake light bulb.
sadly, I couldn't figure it out.