I am sure this answer might be in here somewhere but i cant find my exact match. Swapping electra glide lollipop taillight for narrower street glide. Electra glide wiring has black/violet each side. Street glide has four wires. White/black/red/ yellow. Not including two license plate white light i will splice into fender cap light.

appreciate help in matching these wires

 

If I had to guess your bike only has turn signal feed (the violet wire?), the new bar (guessing aftermarket, not Harley) most likely has stop tail and turn.

I would jump the wires on the new bar to a battery You can use a 9v if your not comfortable using the bike battery, if it is stop tail and turn two will be brighter (guessing red and yellow) than one (maybe white). Black should be ground but if it’s Chinese white could be.

If correct you can hook your violet wire to red or yellow and then your bikes black to the ground on the bar. The other wires would be unused as your bike doesn’t have feeds for them.