Check the four way flashers to see if they work first. If they work then no doubt about the wiring or bulb circuits. Post the results so others may benefit, whatever the outcome. Good luck, hope you get it fixed!
Check for battery voltage at the brake light switch next! If no voltage there on either wire, recheck fuses with a test light to be SURE you didn't miss one that is bad! If there IS battery voltage at the brake light switch, push pedal to see if voltage at both wires then, if so you still have a signal switch problem. One more thing, does anything work that is controlled by the combination/signal switch like the wipers?
Ok read very carefully. The Dimmer switch is more than likely the problem. Disconnect negative Battery cable. Place a Light attached wire to 2 alligator clips between the Battery post & the cable. The light should come on. Remove under hood light if have one. Close all doors & all power off at ignition switch. The jumper light should be on. After a minute it should go off. That is part of the security & lighting delay. If it does not go off? Get into car. wait again for jumper light to go off. Can be done one of 2 ways to find a short. Start pulling fuses at Glove compartment block. Check light after each fuse is pulled. Or start disconnecting at switches or light sockets. I found that the Eye level brake lights get wet. pain to get to by laying in truck with all the carpet etc. removed. It is a long drawn out process. It took me 2 days of disconnecting circuits. So I did it at night so it was cooler & could see lights if on or off. The cover on Steering Column is held with screws. Torqx. Remove it. the ignition switch & dimmer switch are easy to get to. I found that the wiring block to the dimmer was melted causing short. Go to junk yard that has your car & start cutting off wiring at were ever you have found a short or melted wires of plastic blocks. Also check the fuse box under hood. It can have problems too. The fuse for Ignition & 4 way flashers is there. Plus all the relays for ABS, Head lights, Heat windows etc.