My brake lights and tail lights on my 2003 Chevy Suburban are not working. The fuses and bulbs are good. The high mount brake light is working but not the lower right and left ones. What should I check next?

Check the ground wires. If you have a towing package or extension to plug in trailer lights, that sometimes is an issue.

Thank you, I will do that.

Good luck, most electricians that try to find shorts are bald from pulling out their hair, or gray from worry. :-)

I true that an I it still don't work

If you can, since the upper lights are on a different line to the rear brake lights, see if you have power to the socket when you step on the lights. And a simple question. There are two types of tail lights. Ones that burn with the parking/driving lights only, and ones that have a second filament in the bulb that activates when the brake is engaged. Make sure you have the correct bulbs, or the wires or bulbs were not switched. If you have power to the socket when the brakes are activated, it is either the connection, socket or check the ground. Like I said, the only thing worse in finding out why a bulb doesn't work, is one that sometimes works and sometimes doesn't. That would be a lose wire. If you have power from the fuse, work past the fuse and follow the wire for power until you either find a break in the wire or the power stops. You just may have to give up and string a new wire all the way back. Does your sensor switch have two wires coming out? Maybe it is the sensor switch working one but not the other. At this stage you have to consider everything. It's time consuming and at times it should be a two person job to check it properly.

John is right. Sounds like he's experienced. 9 out of 10 times, its a ground wire at a connection point. Loose, rust, dirt, corrosion, pinched, usually at the towing extension lead if applicable, spare tire crank area, or left to right parallel connection point.

I was assuming he installed the correct bulbs, but before you run a new wire, (which sometimes can be easier, but usually not), CHECK ALL YOUR CONNECTIONS... Top & bottom running wires. Don't just look at them but wiggle them while using a voltage meter. Hopefully the vehicle in question didn't spend too much time by any great amount of salt.Utah, costal cities, or snow areas where they put salt on the road to chemically melt the snow. Thats when sensors start acting up.