So my brother got these dark taillights for his BMW car. Unfortunately the bulb for the fog light is missing. Actually it isn't possible to install a bulb as it's not prepared for it.
Now I needed to solve this somehow. And as I've been meaning to look into LED lighting for some time I used this as an excuse to make one.

First here is the schematic:

So how's it work? Easy. The current for the LEDs is controlled by Q1. Q2 works as an overcurrent switch and controls Q1.
And the current itself is set by calculating R2 = 0.5V divided by the wanted current.

Here are some photos I made of the circuit. I know it's a bit primitive, but it gets the job done.

fog_front fog_back fog_control

Here is the list of items I've used:
LED1-LED5 = Red 5mm 17000mcd power LED
R1 = 100K
R2 = 5R (0.5/100mA)
Q2 = BC547B

I got my LEDs at You will probably be able to find a shop dealing LEDs near you too.
And although I would love to have come up with the circuit on my own, I'll admit to have found it on the Internet at