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?