The diode allows current to flow to the rear brake warning light when you activate the starter motor as a way of checking that the brake warning bulb is not burned out. Other wise known as a bulb check. The purpose of the diode is to prevent the brake light warning switch in the rear brake from operating the starter motor when it closes due to low brake shoes.....
So, what this means is if the diode is shorted out and the brakes get worn a little too much, the bike will start itself when you turn on the key, but you won't be able to stop the bike because the brakes are worn out......
This whole misguided Rube Goldberg, Ralph Nader mess was discontinued the following year, but Rube and Ralph didn't give up trying to save you from yourself. Oh, no.......not a chance..
... they came back with the '80's models with very elaborate wiring and safety features that actually prevented you from starting the engine so you could just stay at home and drink beer...
Staying home and drinking beer could lead to issues with the wife and the family dog that could get out of hand and end up with you being in jail, but that's OK with Rube and Ralph because now you could get the help you need, like anger management counseling and substance abuse therapy.
After 30 days in jail, you would be curred and no longer have the irrational urge to ride your motorcycle, which you can't start anyway, so you would put an ad in Craig's List to sell the bike, but in your altered mental state, you put the ad in the sex for sale section by mistake....
..... and that really got you back in trouble with the wife when those hot babes came around wanting to check out the soft leather on the seat of your non functioning XS650..
....but....Rube and Ralph are happy, and that's all that matters...
(Now you have the time to settle out of court with PETA regarding the issue you had with the family dog....
)
