LED Brake Light and Turn Signal Mod

[BusaWhipped]

I put an aftermarket undertail on the Busa last August prepping Luci for the track. The standard Hot Bodies undertail has a couple of LED pucks they use for tail lights, brake lights, and turn signals. I wasn't thrilled with how difficult they are to see during the day. The undertail also doesn't have licence plate lights which are required in Missouri. Additionally, replacing filament bulbs with LEDs causes other problems because of the lack of resistance. The turn signal flash rate will be way too fast and if you have a Cruise Control, it will stop functioning. Before I go through the step by step, here's a short video.

Before and after the mod

 

[BusaWhipped]

First thing was to remove the undertail so I could work in the comfort of the house

 

[BusaWhipped]

The LED pucks were just glued into the undertail, so a little box cutter work and force and out they came. I cut a couple of disks out of some scrap ABS plastic sheet, drilled a dozen holes in each and welded them into the gaping holes left by the removal of the disks. In the photos, the new LEDs are sitting in the holes. I had to paint the rear of the undertail black again since I only have white plastic stock.

 

[BusaWhipped]

Once the paint dried, I installed the LEDs and soldered up the connections. The wire leads you see in the picture were for bench testing the LED connections before getting too far into the build. The tail light run through 2.2K and 430 ohm resistors. The brake light and turn signals run through 430 ohm resistors.

 

[BusaWhipped]

After a successful bench test, I removed the test leads and added a taillight integrator. The one I bought was less than $20 at the Uhaul store. The integrator allows you to use the same wire for the brake light and a turn signal. To insulate the wires and hold everything in place, I burried the LEDs in black silicone and made silicone straps for the integrator unit. Other than adding the connectors on the other end of the integrator unit to match the stock connectors on the bike, that completes replacing the LED tail/brake/turn lights. Now onto the other problems...

 

[BusaWhipped]

For the license plate lights, I installed 2 white LEDs using panel mount holders, connected them to the tail light circuit through a 2.2K resistor, and burried everything in black silicone. I was debating how close to the License plate mount I should put them, and think I chose the wrong position. I think they should be 1/2" further back from the plate mount, but its staying the way it is for now.

 

[BusaWhipped]

From the inside. You can see at the connector where the wires have been doubled up for the tail light and ground to power the license plate lights.

 

[BusaWhipped]

Now to address the issues that don't involve installing LEDs. First the turn signals. The speed at which the flasher opens and closes the circuit is dependent on the amount of current drawn by the turn signals. Since LEDs don't draw as much current as a filament bulb, the flash rate goes way up. So to fix this, I installed two 5 ohm 10 watt resistors, one for each turn signal circuit. Unlike the resistors for the LEDs which are wired in series with the LEDs, these resistors need to be wired in parallel with the LEDs.

The final thing to fix is the cruise control. I have a few long rides planned, so this is a must. The fix is the same as for the turn signal flash rate. The only difference is the size of the resistor. For the cruise control unit to work properly, it requires the brake light circuit to complete the ground. It is very tempermentat with regard to the ohms range that it will operate in. It also has a fairly high current draw, so more watts is better for keeping the resistor from getting too hot. What I installed based on the cruise control requirements and what I could find is a 6.2 ohm 25 watt resistor in parallel in the brake circuit.

I strapped the resistors to the cross bar on the subframe where the seat latch is located using 1 1/2" hose clamps. Next time I pull the entire tail off, I'll look at moving them somewhere a little more potected.

 

[BusaWizard]

Nice work.