The backstory: When I first put this bike together it was eating brake light bulbs. I figured that it was the vibrations and I slapped an LED array in the cat-eye and called it good. Then my buddy said, "hey, why were you flashing the brake light when you were leaving the other night?" I figured out the spring that holds the lever tight to the brake light switch was weak. At that time, I couldn't seem to find a good part number for it, but found a stiffer spring inside another set of hand controls that I had laying around. The brake light quit flashing all the time. I get enough reports of my brake light flashing when I hit a bump(it's a rigid) and when I take my hands to cruise on a nice piece of straight highway(a non MSF-endorsed technique) that I'm pretty sure I need a better spring.
Everyone hates the brake light switch in these style controls, but mine hasn't quit yet.
E-clip and washer on the pivot post.
Push out the pivot post.
Here's the spring that should hold the lever tight to the switch.
I thought I could find a substitute in the Harbor Freight assortment, but nothing was better.
I found a part number and supposedly OEM NOS on ebay.
Replace and reverse steps to install.
I went ahead and measured a new one in case it still wasn't stiff enough and maybe I could find a stiffer one if needed.
I took it for a group ride and it still flashes on bumps. So I ordered this from McMaster-Carr. Going from a Wire Diameter of 0.035 inch to 0.051 should do the trick. I will know in a week or so.