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Rear brakelight switch re-build
15 minutes to save $$$
The time will come when your brake lights just wont go off.

With luck it is the rear brakelight switch connected to the foot pedal for the rear brake, as this unit is quickly and easily repairable in about 15 minutes and just 2 tools!

Figures #1 and #2 at right show the parts of this switch, the main body in white, the top "plug" in grey, the spring in red, the plunger in black and the electrical contacts in gold.

Pressing down on the brake pedal pulls the plunger down by the spring attached between the pedal and switch, bringing the brass band around the top of the plunger down to the level of the contacts turning the brake lights on.
Release the pedal and the plunger rises up with help of the internal spring (in red), and the brass band is again moved away from the contacts turning the lights off.

Normally the problem with this switch "sticking" and leaveing the brake lights on is one of two things...

!. Dirt working into the opening between the plunger and main body.

2. The spring has broken or rusted away or broken.

Either of these problems is easily fixed with two VERY basic tools.

1. Small screwdriver or knife tip
2. needlenose pliars OR diagonal cutters  
Unplug the wires between the brake switch and wireing harness, unhook spring from plunger and pull ENTIRE switch assembly from bracket on frame.

STEP 2 :

Look at topmost part of the body and locate the two tabs sticking through from the plug that hold the plug in place, useing a screwdriver or knife tio GENTLY pry the body outward at these points to allow the tabs past the notches they rest in while working the plug out of the top of the body.
(Be carefull not to drop and lose the spring in case it is still good)

STEP 3 :

CLEAN EVERYTHING ! The contacts and the band on the plunger may be cleaned up with steel wool or some very fine sand paper, clean the rest with some WD-40 or whatever solvent/cleaner you have on hand that will not harm the plastic.

STEP 4 :

Inspect the spring that was found around the small part or "arm" the plunger, if it is rusted or broken get a new one, right in your pocket!
A spring from a common ball point pen is the same size and just as strong as the factory original, just a tad too long !

Useing the cutting part of your needlenose (or your diagonal cutters if that is what you are useing) remove about 3/16 - 1/4 inch from one end of the pen spring.
This is an APPROXIMATE amount only as springs and switch bodies may have slight dimensional differences!
Use trial fittings to see that plug fits firmly back into place and that plunger has enough travel to make contact, trimming the spring as needed.

STEP 5 :

Re-assemble and replace on bike (reverse steps #'s 1 and 2)
some re-adjustment of the switch in its bracket may be in order to get brake lights to come on at the point you wish them to in relation to your brake pedal position.

Your ready to rock N roll !

Note :

If on dis-assembling the switch, it is free of grit that is stopping proper function and spring is in good condition, check that there is not excessive wear on the contacting points of the band and contacts.
Also that the wires are securely soldered to the contact plates.

If new contacts are needed, some may be made out of light brass, the brass plate found in an old flashlight should be about right to make some new ones from with a snips, a file and pair of pliars, and then soldered to the wire leads for the wireing harness.