How to change 3rd brake light on 99 buick - 1999 Buick LeSabre

Sounds like your brake light switch is going bad. The 3rd or high mount stop light is separate from the regular brake lights otherwise it would flash with the turn signal so it has a separate circuit in the same switch. I hope this helps. Take care.

Hi,
If you check the brake switch first, pull connecter off and see if you have 12 volts on one side of the plug. if you have power use a small cotter pin and jump the connector the brake light should come on with the 3rd brake light also. If that doesn't work more than likely its your turn signal switch that is the culprit.

Check your third brake light

Hi William, To begin, the usual color coding on American vehicles is black is ground. To test this, take a long length of cable and a test light. Connect one side of the test light to battery positive and and the other cable connect to the black wires one at a time. If the light comes on normally you have proved the ground connection, then do the same with the other. Next connect the test light to the green cable and the other cable to the black. Press the brake pedal and observe if the light illuminates. If all is well, connect the black cable from the third brake light to the black cable of your car and the red cable from the after market brake light to one green cable from your car an insulate the other. Then go ahead and mount the third brake light. Regards John

my 02 has 2 nuts in the trunk then it will lift out of the cat walk

sounds like your brake light switch took a shot this is located on the brake pedal itself i would replace all brake light bulbs and switch to resolve your issue

If the third brake light works and the regular ones don't, it is most likely a bad turn signal (multifunction) switch. The switch is able to kill the brakes lights to run the turn signals, and in rare circumstances does this. I've seen it several times. It could also be wiring, especially near the turn signal switch, but it is usually the switch.

I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!

Sounds like a broken wire somewhere.
Since the middle brake light works I would suspect it is somewhere in the trunk or close to the back seat.
Buy or make a tester. A 12v light with a clip on one wire that you clip to a good ground on the car the other wire with a sharp point. Turn the turn signals on then poke wire to rear lights until tester lights. When tester lights you know the break is somewhere inbetween the tester and the brake lights.

Hope this helps.

Stan

Look in the owners manual...it should have access instructions for this bulb. Or, try calling (or stop by) a dealer. the "service consultant" or service manager should be able to quickly tell you how to access the bulb.