Bike tail light issues (video included)

[OMCC]

So I had to remove my rear fender and disconnect my tail light/flashers to change my rear tire. The P/o replaced the stock fender and lights with a harley one making it necessary to remove it during a tire change. and the wiring the P/o had put together was a little jankey so I began to replace the 16awg wire with 14awg wire. After I hooked up the tail light I wanted to check to make sure the wiring was working so I connected the tail light exactly how it had been when I disconnected it. nothing happen so I started experimenting thinking that maybe I mis wrote the wire routing when I disconnected it. when I connected the taillight "black" wire to either of the flashers wires from the bike, the taillight and opposing light would work perfectly.

Video of issue here
https://www.youtube.com/watch?v=tLjNxmwBOBs

So I'm thinking the issue is the black wire coming from the bike but I don't quite understand what would make the wire all of a sudden stop working. it was working perfectly before I removed it for the tire change.

[rdmcguy]

grounded?

Not being sure of what wires are connected to what wires (color wise)
and not knowing how many wires Harley taillight has (two or three) my first guess would be that taillight needs to be GROUNDED to something .which appears to be happening through front turn signals .if you get my meaning ...so either remount rear fender or provide temporary ground
...hope that helps

[OMCC]

This was it thank you so much