Monday, January 3, 2011

LED turn signal upgrade on motorcycle (Ducati S4RS)

This shows you how to upgrade your bulb turn signals with LED aftermarket ones. In my case I picked some short arrow shaped ones and in the process, I changed the tail cover of my motorcycle. First let's talk electrical circuit. What applies to everybody here is the fact that you need to restore the circuit wattage since LED consume considerable less power than bulbs. In my case the Ducati S4RS does not expose the relay that controls the turn signals so there was no option to simply replace the relay with one appropriate for LEDs. In my case the individual turn signal would go from 10 watt for the bulb based to 0.7 watt for the LED based. For all practical purpose I ignored the 0.7 watt and just computed how much Ohm do I need to replace the 10 watt. Using the Ohm law it worked out to 10 watt, 10 Ohm.

my DIY version


ready made and sold by


Radio Shack happens to sell exactly those spec. You will need one per bulb ou replace. Some soldering, wired and shrink plastic tubing it is all you need to package it neatly. Add a couple connectors, actually make it into a bypass and you are done. If you are not the DIY type, I suggest, they have this very same set up ready to go.

Aside: the resistors for the front.

The resistors for the front needs some special attention since they will be exposed to the elements. So I am creating an overlap on the top and folding it onto itself to create a sealed end. Installing this vertically with the sealed end on the top (wires exits from the bottom) will ensure that no water or moisture can get inside.

The rear

Note: the resistor in this case fit into a nearly sealed compartment inside the CF tail along with all the wire connectors. So this installation is a little easier since there is no concern of the electrical component being exposed to the elements.

The rear turn signals are installed by connecting them together using a rubber hose and clamping them between the tail light assembly and the license plate frame. Cutting a small opening in the middle of the hose will allow the wires to come out. The whole assembly results in a solid rubber mount that is reminiscent with pretty much anything on this bike since pretty much everything other than the handlebar is rubber mounted.

The front

Here are the DIY CF braces to install the LED turn signals on the front of the bike. These were made using a 1'X1' CF tubing cut with a Dremel. I used card board to mock up the part and to get a template for the holes. Just measure twice and cut/drill once ;-)


The final installation



  1. Great start, but would you be willing to provide more detailed information? I have 4 new LED signals (2 front and 2 back). Did you need to install one resistor with each signal? So you would need a total of 4 resistors? Also did you just place the resistor in between the original signal wiring and the new LED?

  2. you only need one resistor dummy load per side. You can probably use a much higher resistance. I developed the FLEDA System ( for the Sport Classics and found that the flash rate circuit is looking for somewhere around 150 ohms per side to make it think the turn signals are working and flash at the normal rate. Try putting a potentiometer in the circuit and adjust it till the turn signals flash at the correct rate. Measure the the value and drop it about 10% to be safe and that the value you will need for your dummy load resistors. Probably a 1 watt will suffice but you can do the math for power dissipation.