First thing I would look at is the operating switch, mounted on the 5-way union (frame rail just to the rear of the RF wheel).
If you are by yourself, probably the easiest test is to temporarily short across the switch with a test lead or similar.
Turn the key on, and the brake lights should come on. If they do, then most likely the switch is bad and will have to be replaced.
If not, check whether power is getting to the switch (preferably with the jumper still in place). If you find power, the next check would be at the brake lights. If not, the problem is somewhere between the switch and the fuse block.