1949 Chevy 3600 Wiring

[mytruck1949]

Guys
need some help here. I am sure it is pretty simple but a rookie to wiring on this old truck. Its a 6volt system. I have 2 wires that ran down the drivers side frame but then draped down to the ground. I have been able to tap into 1 wire that shows 6 volt and run it pig tailed to both lights. Pull the headlight switch on and I have lights. whohoo.

Now onto what I do with the Black wires from each tail light?

Also any clue what the second wire is that ran in tandom with the hot wire. I put the meter on it and I get nothing. I had the misses step on the brake and nothing.

any advice you have would be great.