My 3rd brake light doesn't work at all. None of the LEDs light.

I checked for power to the harness - when the brake pedal is depressed there's voltage at the end of the plug going to the light. But the lights don't light.

I pulled the light out and applied direct battery via leads to the light itself - nothing. None of the LEDs power up.

The other brake lights work (as do headlamps, fog lamps (front and rear), etc.

The light looks extremely simple - there seems to be a black diode or something between power and the LEDs so I'm assuming that's dead. I'm no electrician so wondering if there's something I'm overlooking or should I just pay the money for a working brake light and be done with it?

 

Anyone?

 

I took it apart because some LEDs were burned out. I bought replacements and put them back in. It's strange that none of them work. I don't remember the exact components now, but there's definitely a resistor (to ensure the correct current flows through the LEDs). If there's also a diode, it's definitely one of those elements (a burnt-out resistor or diode). To test it in sections, you can safely perform a test with a 9V battery (the kind used in transistors).

 

When you rigged a separate 12v supply to test the assembly, did you also rig a separate ground wire or just use the one fitted in the car?

 

No, I tested it outside the car. I used a 9V battery like the ones used in transistor radios, so there's no risk of damaging anything. There are only two wires, positive and negative, which connect to the 9V battery (you can use alligator clips).
Since disassembling and reassembling the third brake light is delicate (though not difficult) due to the fragility of the retaining clips and the housing itself, I'm not taking mine apart right now. But with the 9V battery, you don't run any risks and you can see if it works.

 

I bought a strip of red leds and replaced the whole led board.

 

Depending on the vehicle inspection regulations, an LED strip may or may not be suitable. By the way, although you've probably already done this, check with a voltmeter or a W5W bulb (not LED) that voltage is reaching the connector when you press the brake pedal. (If you use a bulb, you can leave it connected and check that it works; if so, the problem is indeed in the third brake light assembly.) You can find these LEDs on eBay or AliExpress. To remove the LEDs (if any are broken), you need to use a desoldering tool (to thoroughly remove the solder) and then resolder them. The same applies if any other component is faulty.