1. First, check to see if you have power going to the brake light switch (BLS). The BLS has two terminals; one of them is always hot (power in). When the brake pedal is depressed, a properly working BLS will allow current to flow out through the other terminal. So if you DO have power going into the BLS with the brake pedal all the way up, and you do NOT have power on the other terminal when the pedal is depressed, the brake light switch is bad. If you DO have power on the other terminal when the pedal is depressed, the problem is further downstream.
2. You need a helper for this step. Next, 'jump' the wires going into the two prong BLS plug. Assuming that one of them tested hot in #1, 'jumping' these together should send power to the brake lights. It's always a good idea to use a jumper wire with an inline fuse, but you gotta do what you gotta do. This is where your helper will come in handy. If there are still no brake lights, with the switch still jumped, pull brake light bulbs and test for power at the sockets (AKA pigtails). If there IS power in the pig tail, but no brake light, it is either a bad bulb or a bad ground. Test the bulbs right on the car battery by grounding the case to the "-" terminal and touching the bumps on the bottom with a jumper wire connected to the "+" terminal. If the bulb tests good, (remember this step assumes there is power to the pigtail), run a jump wire from a known good ground to actually touch the bulb casing while it is in the pigtail. If you DID have power to the pigtail, #2 should fix it.
3. If after step one you DO have power flowing out of the BLS, but there is no power in the back at all, you have a break in continuity somewhere. Check all plug ins (you will need a wiring diagram). Many people don't know that brake lights go through the turn signal switch and cancelling cam. The turn signal cancelling cam (TSCC) has 4 wires on the back side of it that stick out enough to make contact with 4 copper bumps under the TSCC. Depending on the position pf the turn signal switch, the wires hit bumps that distribute power to the appropriate brake light bulb. You have to pull the steering wheel for this, but it is no big deal. Try steps 1 and 2 and if you still have no brake lights, I will post text and pictures for step #3.