Before you go crazy tearing things apart trying to locate the problem, try this: I was ticked because i thought my light wasn't coming on when I squeezed the front brake. Try squeezing it REAL hard, like you were coming to a hell of a stop. I know this sounds simple, but it might be it. I noticed with my 620, a tiny bit of pressure on the rear brake will turn the light on, the front brake has to be squeezed almost as far as it'll go to turn on the brake. Hope this helps.