Motorcycle Repair: Brake light switch failure, hydraulic actuation, brake light switch

Question
Chris,
I recently acquired a 1988 Yamaha FZ750.  The front brake was not turning on the brake lights so I fitted a generic brake light switch into the hydraulic line an they worked - but only for a month.  The brake fluid is very old and dirty and I know I must replace it, but could the old fluid have caused the original switch AND the new switch to fail?
Thanks in advance,
Tom  

Answer
Hi Tom.
 Most brake light switches on motorcycles do not come in direct contact with the brake fluid and would not be affected by it.  However, any electrical component, no matter where on the bike, that is in direct contact with any of the fluids in the bike will be affected by the quality of the fluid.

 Now, I have never worked on the FZ series at all, but the basics do not change.  As I said before, most bikes have a mechanically actuated switch for the brakelights that is directly connected to the brake pedal, but your description says that your bike has a hydraulic actuation.

 This type of switch would rely on pressure in the line to activate.  There would also be a couple of other factors involved, here;  Those being cleanliness of the fluid and a properly bled system.  An air bubble in the line could come in contact with the switch and air will compress, where brakefluid will not, or if the switch is attatched to the outside of the line (relying on line expansion to activate), then any air trapped in the system would prevent that from happening.  Thus the switch would be disabled by a simple air bubble.

You should go ahead and flush the system and change the fluid, since it appears to be overdue anyway.  Then properly bleed the system and see what happens.  BTW, you should get an OEM switch for the system, since that is what it was is supposed to be there.

 When you look at a problem like this, just apply basic deductive reasoning and some high school science and you can usually figure it out fairly quickly.  But even I get stumped, sometimes when I work on my own bike, so don't feel bad about it if you get stumped once in a while by a seemingly simple problem.  It happens to everyone.

Good luck.
FALCON