My motorcycle has a Givi model E52 trunk that has integral brake lights to augment the bike's existing brake lights. The E52 uses 12 incandescent bulbs that take quite a bit of power (on the order of 10 to 15 Amps). By replacing these incandescent bulbs with LEDs I was able to reduce the current requirement to about 50 mA. There is much less heat generated which is better for the plastic case and the LEDs will have a very long lifetime when compared to the life of incandescent bulbs.

Step 1: Project Tools and Supplies

For this project you will need:

1) A philips screwdriver
2) A soldering iron and solder
3) An Xacto hobby knife (for cutting circuit board traces)
4) 12 x Red LED -- high-brightness (e.g. Digikey Part # 160-1620-ND)
5) 2 x 50 Ohm resistors
6) A motorcycle or scooter with Givi E52 installed (not shown here ;-)

Optional but very handy to have:

7) circuit board vice (a third hand)
8) digital multimeter (DMM) useful if debugging is needed

Step 2: Remove the Diffusers

First remove the two plastic lamp cover/diffuser. There are 2 screws holding each diffuser (4 screws altogether).

Step 3: Case With Diffusers Removed

Here's what the trunk looks like with both diffusers removed.

Step 4: Reflector Front Close-Up

Here's a close-up of one of the reflectors showing the 6 incandescent bulbs.

Step 5: Disassemble Reflector

And here's the back of one of the reflectors showing the circuit board that holds the bulbs. We will be modifying this circuit board to accept LEDs.

Step 6: Original Circuit Schematic

Here's the original circuit.

Step 7: LED Circuit Schematic

Here's the new circuit. We will modify the old circuit board to implement this circuit.

The LEDs that I used have a forward drop of 1.8V, so 6 of them is 10.8V leaving 1.2V across the resistor. A 50 Ohm load resistor results in 24 mA (=1.2/50) of forward current in the LEDs. For higher brightness, use a lower resistor value, but be careful not to exceed the LED's forward current rating.

Step 8: Planning the Board Mods

Here's a picture of the original circuit board. The magic-marker "+" and "-" marks indicate the +12V and ground circuit board traces. The "x"s mark locations where we will use an Xacto knife to cut the circuit board traces. This picture also shows where the resistor and wire jumper need to be added. Before cutting any traces, first use a soldering iron to remove the incandescent bulbs. You may need to use some solder wick to remove the old solder.

Step 9: Board Mods

Here's the modified board. Be very careful of polarity when installing the LEDs. If you install them backwards, they will not light. Refer to your LED data sheet for determining polarity. Typically there will be a flat side on the LED plastic lens and/or a shorter lead that will indicate the cathode. Current flows from the anode to the cathode, so the LED cathode must connect to the lower voltage.

Step 10: LEDs Installed

Here's the front of the circuit board showing the LEDs installed. At this stage it is ready to be tested.
Just plug it in and step on the brake. If it doesn't light, go back and check all the circuit board cuts and connections. A DMM (Digital Multi-Meter) can be very handy at this point to verify all of the connections.

Once you have one circuit board working, repeat the same modification procedure for the second circuit board.

Step 11: Button It Up

After both circuit boards are modded and tested, then reassemble everything and you're done :-)

Step 12: Future Ideas

Running lights are an important safety addition for motorcycles, and because LEDs require very little power and generate very little heat, it is possible to use them as a combined running-lights and brake lights.

Here's a hypothetical circuit to use the newly added LEDs as combined running and brake lights . I have not tried this, but it should work. For this circuit, with the brake switch off, the LED forward current will be about 18 mA and when you hit the brakes, the LED forward current will rise to about 33 mA resulting in a brighter LED output. The final resistor values used may need to be adjusted to get a good compromise of reasonable running light brightness and adequate brightness modulation when the brakes are applied.