Usually by the brake light will be a quick disconnect on the wires. Your brake light should have three wires. One for ground, one for running light, and one for brake light when you activate the brakes. To figure out which wire is which:
Ground should be the black wire.
With the bike off disconnect one of the other wires.
Turn the bike on, if you don't have running lights that was the running lights wire.
Otherwise it was the brake wire, activate the brakes to verify.
Take a note of the color of the wire and find it under your seat.
Connect the wire back up.
2000 Yamaha Vstar Classic 650
2013 Victory Cross Country