My 2008 Sportster rear brake light switch quit working. I checked my repair manual which gave alot of information for early models with the brake light switch on a plunger from the rear brake linkage. The late models like my '08 have the switch mounted on the rear master cylinder. The book only gave one sentence of information and left the rest to me. I checked the magic box (internet) and found a little more but still nothing very substantial. Hopefully this instructable will help fix that problem. Let's get started.
Step 1: Secure the Bike
Ok folks, to do this your bike needs to be straight up not resting on the side stand. I use my front tire chock. You can put it up on a lift or just brace up the frame with blocks and use a tie down straps to secure it. I used the tire chock and blocks under the frame.
Step 2: Find the Switch
The rear brake light switch is behind the brake fluid reservoir on the left side of the bike. Below the side panel, between the motor and rear tire. Do you see it hiding back in there? Sorry the close up pictures are a little out of focus.
Step 3: Remove the Cover
The reservoir needs to be taken loose so you can move it aside and get to the switch. First you have to remove the reservoir cover. This is simple because the cover just snaps on and off. Give it a tug and see for youself.
Step 4: Release the Reservoir
Now loosen the reservoir. Mine was a 3/16" allen head bolt. With the bolt out the reservoir is only attached by a rubber hose. It will move just enough to allow you to reach the switch.
Step 5: See It Now?
Do you see it now? Oops I forgot you have to buy a new switch before you start... but you knew that already didn't you?
Step 6: Unplug
Unplug the wire connector.
Step 7: Out With the Old
Now using an open end 11/16" wrench, take the bad switch out. I wasn't sure if brake fluid was going to spit out all over the place so I put my drain pan underneath. Turns out it dripped once or twice and that was it. The shop rag caught it all.
Step 8: In With the New
Next I put a little thread locker on the new switch and installed it. I used red, high strength, thread locker because it looks like that was what the factory used. Don't put it close to the end. You don't want any lock compoud contaminating the brake fluid.
Step 9: Plug In
Now re-attach that wire connector.
Step 10: Bolt, Bleed, and Cover
Put the reservoir back. I used medium duty, blue thread locker on the bolt. You will need to bleed the brakes. When you take the old switch out it lets air in. If you try the brakes now the switch won't work because with air in the system the pressure will not be high enough to activate the new switch. I haven't included brake bleeding here because there is plenty of information out there on how to do that. With the brakes bled properly, re-install the reservoir cover... just snap it in place.
Step 11: Light On
Now turn on the ignition and try the brake pedal. The light will come on. With these types of switches there is no adjustment like the older models that work from the brake linkage. Time to ride to the local pub and celebrate your success. I'm pullin' for you... we're all in this together.