Hi
I have ford focus mk1. I have just replaced the 3rd brake light with a clear Lexus style LED light, but it doesn't seem to work. The connection is exactly the same as the previous light. The only difference is that it's LED.
Any ideas why it won't work?
Cheers

 

As a led light, you should check the polarity first.
if you connected it with a pair of wires, just swap them over

 

So is it a case of connecting the red wire from the light to the black wire on the car, and vice versa?

 

if you can get a hold on a multimeter you can try to find which wire is positive and connect it to the red wire on the led.

The only way a car "might" have a black wire for positive is if it has all its negatives a different color. On old fords the negatives were brown, but I have no idea what colors your car has.

Because the led is as its name suggests (Light Emitting Diode) is a diode, if it is connected the wrong way, no harm will be done, but it wont work.