Chevrolet Repair: 99 Chev Suburban brake lights, turn signal switch, brake light switch

Question
Our brake lights appeared to be out so James replaced the fuse, the tail light bulbs, and down the panel the lights are connected to.  When we went to check them, they seemed to be out, then they worked and then they didn't.  It seems to have a some kind've wiring problem.  Where should we check first to find out where the problem is?

Answer
ok Catherine and james...lets fix it....The brake light circuit is the same as the 4 way emergency flashers circuit. So lets turn on the hazard lights and see if the rear ones flash. If they do, we are going to go under the dash and check the brake light switch. The brake light switch has two wires. one is 12 volts the other carries the 12 volts to the turn signal switch.When you push the brake pedal both sides of the switch must have 12 volts.The turn signal switch isolates one side to ''pulse as a turn signal. If the brake light switch is mis-adjusted or stuck in the open position you will get no brake lights at all.If the turn signals don't work you have a bad turn signal switch...confused? don't be...Now go fix it!.....Best!