This DIY applies to Pre 09/2001 production coupe BMWs. It is possible to do it on later cars but there's no need since the LCM can be reprogrammed to accommodate LEDs.

There are a couple of things to have in mind:

1. OEM Leds are used for this mod, not aftermarket ones. LEDs from M3 will fit the Coupe and vice versa.

2. This mod requires cutting and soldering wires, if you are not familiar with soldering and capacitor/resistor values, take the schematics to somebody who knows how to and relief yourself from smoke/electric shock etc. I did the mod with a friend of mine who is an electronics engineer just to be on the safe side.

3. In addition to the OEM led clusters, you will need to obtain the corresponding adapters from BMW or eBay. These adapters convert the car's plugs for use on LED clusters. Beware as the adapters are specific for LEFT side and RIGHT side clusters. If you put the adaptor in the wrong side, nothing will work. They are clearly marked with left and right anyway.

4. The LCM or Light Control Module checks if a bulb is burnt by sending a 3-volt pulse every minute to the front and rear lights. This pulse, is not strong enough to light the standard filament bulbs that you have, but it's enough to briefly light the LEDs. Therefore, every minute you will see them flashing. To remove this flashing, I had to create a filter that would route the pulse to the car's chassis (ground). You need 6 filtering systems.

a. Left Blinker (Green/Blue)
b. Left parking light (Green/Black)
c. Left Brake light (Light Purple/Dark Purple)
d. Right Blinker (Green/Blue)
e. Right parking light (Green/Black)
f. Right Brake light (Light Purple/Dark Purple)

5. Additionally, load resistors must be used to trick the LCM that you have normal bulbs behind you, or else you will get the "bulb out" error on the instrument cluster.

6. I used resistors with integrated heatsinks safely secured on a large aluminum block with CPU heatpaste between them for optimal heat dissipation. Heatsinks provide a good way to remove the heat generated when lights are in operation. The values have been calculated by measuring current and original bulb resistance. Less wattage resistors can be used but they will get hotter, so I suggest using the ones I did. For wiring, I used thick ribbon wires with good insulation.

Parts List:
a. 6 x 50w / 33 Ohm; Resistors with Heatsinks
b. 6 x 10w / 10 Ohm; Resistors with Heatisinks
c. 6 x 470 uF / 25v Capacitors
d. CPU Heatpaste (Optional but recommended)
e. Aluminum Block (25cm x 15cm) with fins
f. Couple of screws
g. Ribbon wires
h. OEM LED adaptors

Cut the 3 wires from each side, and route connect them as the schematics below.

3 wires on each side to be cut:

OEM Led Adaptors

LCM

General Schematics

Circuit

Wires From Left. Later on I carefully placed them under the rear trunk trim.

From Right:

Aluminum Block

Complete System:

Later on, I discovered that my rear brake lights are constantly on when I turn on the driving lights. This is because there is a constant 5v current running through the rear lighting system. I assume that this voltage works as a pre-heat for filament based bulbs in order to light up quick and prevent premature failure. The 5v current is not enough to light a filament bulb but was strong enough to light the LEDs.

In order to "remove" this 5v current, I routed the brake line to a 12v relay. The 5v current is not enough to close the relay and therefore the brake lights remain off. When I press the brake pedal and 12v come through the wires, relay closes and brake lights operate properly. This does not affect in any way the instantaneous LED light up.