Modern Buddy

Recently I found that the interlock that requires one of the brakes to be engaged for the starter to operate, was not working when I was squeezing only the left brake lever. Not a big deal: squeezing the right brake lever and pushing the starter button is a little awkward, but easy enough. And with a little experimentation, I discovered that if I squeezed the left lever halfway, the interlock engaged and the starter worked.

But then I noticed that the same thing was happening with the brake light: coming on whenever I squeezed the right lever, and also when I half-squeezed the left, but not when only the left lever was fully engaged. Makes sense to have the brake light on the same circuit as the starter, because they're enabled by the same action. Still not a crisis – I almost always apply both brakes together, so there aren't a lot of situations (other than starting it) in which I'd have the left lever fully squeezed by itself – but having the brake light turn off like that is still a bit of a safety hazard, especially this time of year when I'm riding in the dark every day.

So... has this happened to anyone else? I can pull out the parts/assembly diagrams and figure out how that feature works, but does anyone have an idea of where I should start looking?

My first thought upon reading this one is that the left hand brake light switch isn't working right anymore. Not sure how much lever movement is needed before the switch plunger energizes the circuit when everything's working properly, but it shouldn't require too much movement. Also, I agree that it could be a safety issue. Either there is corrosion in the brake light switch or the switch has failed internally. It'll be in the headset, fitted into the left-hand brake perch. The switch shouldn't be too pricey.