2003 Chevy Express 3500 Brake Loose Connector??

I have a Chevy Express 3500 fifteen passenger van. Recently the brake light started alarming every time I hit a bump. Then when I hit another bump it will turn off (or not depending on how big the bump was). I already topped off the brake reservoir with fluid, but it still does the same thing. What else can I do to troubleshoot this intermittent problem. Of course when the vehicle is at a stop, the alarm will not sound so it makes it even more difficult to wiggle wires or such to troubleshoot when not moving. Please advise. Thanks

Eric