3rd brake light on the trunk is not working the other 2 are

There is often a switch on the brake pedal lever which lights the Brakes up. On some cars it is a electric fitting off the Master cylinder under the hood.

Sometimes the wiring disconnects in the trunk, and power is interrupted. It is not impossible for both Brake light bulbs to burn out at once, but the 3rd safety brake light would suggest that if it works the problem is rearward and if the 3rd light does not, the problem is forward.

Use a voltmeter to test for power.

The plate lights are connected with the park lamp circuit and it is Possible that the GROUND connection to the ligh assembly has failed or it can be the lamp holder that has failed.

Poor Ground / CONNECTION on Junction PLUG Located In Trunk on the HARNESS For All REAR LIGHTS, This IS VERY COMMON.

in the trunk or the 3rd brake light? trunk: remove the carpet cover, then 10mm bolts or wing nuts, pull tail light assembly out, twist bulb to remove. 3rd light. lay on your back in the trunk, locate and remove 2 10mm nuts, crawl into back seat pull up on housing. there will be a long plastic tab that will prevent you from pulling the housing all the way out, you can cut this and make this procedure easier, or remove the entire hat rack.

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

I had the same problem with a 91 mazda 626. turned out that the wires that ran from the lights along the trunk and back into the harness were broken from opening/closing the trunk. i would check around that area first.

If your third brake light is working, then we know it is not the brake switch. Get a test light and check to see if you have power at the light socket. If power is present possible bad ground. If no power, check connections inside of the trunk. Also choose a spot just behind the back seat to be sure that power is on the brake light wire, this will check for possible break along wire.

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

Hi

I had a similar problem on my e270 cdi and fixed this by earthing the 3rd brake light . This has solved the problem . No more errors like : 3dr brake light and numbret plate light malfunction ...

Aubrey
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This is how i did it on my 2006 Sonata

1.) unplug the connector in the trunk (its a small white plug running up to the third light, there should be a small clip you squeeze).

2.) remove the 2 gold-colored screws from inside the trunk. They can be seen from the trunk. 1 is thru the larger square opening where the wire connects to the 3rd brake light. The 2nd is on the right side thru a small (screwdriver width) hole covered by a piece of foam tape stuff I had to punch me screwdriver through the foam to get to it.

3.) after removing the 2 screws, go inside the cabin and the brake light housing pops up.

4.) disconnect the bulb from the housing while inside the cabin (I had to do this with me two forefingers since the housing only pops up and inch or two).

5.) in the trunk remove the wire and bulb. (it's about 5 inches long. the wire from the connector to the bulb socket)

6.) reverse steps to install.

It is a pain and reqiuires a bit of time only because there isn't a lot of room to move around, but it beats taking it to the dealershio!