Third Brake Light Question

[jeremy manlief]

Did a search and didnt find much. I found out that my third brake light wasnt working. The last time I remember, it was working. I took off the spoiler and removed it to inspect it. Everything looks good and I am getting power to the harness when the brake is applied. Has anybody fixed there third brake light? I know that LEDS normally dont go bad, but when all are out, I think that would be rare. There seems to be a resistor inline with the harness on the lamp housing itself and I know you need a resistor for a LED to work. Could that be bad or is the problem inside the housing.

 

[seraphiem]

If I remember right the third brake light is a series of LED banks wired in series and parallel. There is a current limiting resistor already in line.

The third brake IIRC was 20 LEDs with 4 banks of 5 LEDs wired in parallel. Each bank was wired in series. That way your voltage drop across all 20 LEDs would be closer to 12 volts then a single LED and the stock current limiting resistor could be quite small in a power rating.

I ended up drilling out each housing of the third brake light and simply wired in 20 T1 (or T1 3/4, cant remember) 5 mm red LEDs in parallel.

Using Ohms law I figured out the new current limiting resistor value at 12 volts and a value of 20 mA. If I remember correctly it was a 600 Ohm resistor with a power rating of a watt.

You can choose to wire up your LEDs anyway you want. Either in series/parallel hybrid like the factory or all in parallel. Just make sure you select the proper resistor value and power rating.

If you need more help I'm sure others and myself can get you through this.

 

[jeremy manlief]

thanks for the info. Im going to see if the resistor went bad. I know that all my LEDs worked the last time i payed attention to it. I thought it might be a simple circuit. If the resistor isnt bad, i guess i will try to open up the housing and see whats going on inside. I would rather repair it since they are hard to find and everybody wants boocoo money for them

 

[SHOtimer]

A few of my LED's burned out. I was lucky to find a SLO in a junkyard with a spoiler and a perfect 3rd brake light.

That part doesn't exist to Ford anymore, what-so-ever.

Doug