1999 Hyundai Tiburon Brake lights don't come on

I assume all bulbs are good. So, you need to start by checking if there is power to the bake light switch. If there is, then actuate the switch to see if there is power out. If there is, then it's time to start tracing the wiring which supplies power to the bulbs. There has to be an open circuit at some point. Also, make sure the ground to the bulb sockets is good.