Rear brake lights not working

At the left frame rail behind the bumper there's a ground connection-remove the black wire.

Now disconnect the negative battery cable. Set your multimeter at 10ohms scale-at the rear light bulb socket, remove all the bulbs-find the dark green wire-put red lead on this and black to each wire on the socket-do you have a reading of any kind and what color is the wire. If so the brake circuit is shorted to that circuit.

Also do this put meter red lead to dark green wire and touch the other to any good ground of the chassis or the ground wire you disconnect earlier do you have a reading if so the brake circuit is shorted to ground. Either you trace the wire or rewired it all the way to the brake swtich.