I have a 1998 Suburban and the right and left signal and brake lights are not working (same bulb). The upper (3rd brake light) works fine. I have replaced the bulbs on both, and checked for cracked/broken wires in the back where I can see the harness/wiring. I didn't think there was a fuse that is for these lights and not the third brake light, but maybe there is?. THanks in advance for any advice.

 

Try looking along the underside of the frame for a junction that your lighting harnesses are connected to. Depending where you live, the junctions can get moisture within them and create corrosion in turn causing a lighting problem. Just pull the weather pack connectors that hook up to the junction and check them for corroded pins or sockets.