I just got my Blazer about two months ago 04/4Dr/4 WD and the license plate lights and 3rd stop light at the top did not work. I am on vacation so I thought I would fix them, well I put two new bulbs in for the plates and nothing! Shouldn't these come on with the head lights? As far as the stop lights go the right and left work fine it's just the stop light bar at the top that doesn't work. Are these LED lights and are they tied in with the right and left stop lights? Any insight will be greatly appreciated.

 

First off, the 3rd tail light is usually a strip of single 5mm LED's. About 15 I would say.

As far as I know, it only goes on when you press the brakes, but it doesn't matter anyway cause it's not working.

It either goes on dim when you turn the lights on and stronger when you press the brakes, or only when you press the brakes.

Continuing on:

You may not like this, but you will have to trace the wire all the way to the battery.

It's the only way to determine the reason it is not going on.

First things first: make sure the lights/assembly works.

Get a long enough wire (as big or bigger than what it has now) and run that from a battery. Use a fuse if you like.

Hook it up to the battery and see if it turns on or not.

This will tell you if it's the fixture or bulbs or wiring in the vehicle.

The license plate lights are easy to test.

Open the tail gate, and pop off the middle plastic threshold thing.

You should see a hole with some wires and one of them has a grommet going down with 2 wires. These are for the license plate lights.

Cut them, then test if they are getting any power. Splice them/posi-lock them back up anyway you want if they work. Now you know it's the BULB or the fixture itself.

You can also just trace the wires to the end of the fixture, take the little plug out and test that, but sometimes it could be the plug itself causing the problem.

Try new bulbs first and check with a digital multi meter before you cut anything.