rear tail lights wiring help

[cjoenny89]

I just installed the wire harness on the back of the truck to get the tail lights and side markers working. I fixed the wire harness at work and installed some better light housings. I hooked up 12 volts and tested the wiring and it was all good,
Brown wire is running lights and that works for side markers, tail lights, and license plate. I also get the blinkers to work.
Left back up light blinks on then off for a quick second when I put the truck in reverse. I am going to make sure I have a good ground on the right back up light tomorrow.
I am wondering is there an adjustment for the reverse light and if so where is it located?
Also I don't have any brake lights. what tells the brake lights to turn on? Is it that single wire under the hood on the proportioning valve that turns on the brake lights? My Brakes are not working good and that is my next issue work on they also might be low on fluid,
so what and where is the reverse switch?
and what turns on the brake lights?
Thanks
Chad