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.