Brake failure light is coming on intermittenly. Have checked brake fluid level, tried pushing pedal all the way to the floor to see if master cylinder is bad- doesn't go to floor. Looked at single wire on block where all brake lines meet under master cylinder- some insulation missing, however wire doesn't appear to be touching anything. With engine on & vehicle parked, I depress brake pedal I hear a noise that sounds like a click, once when I press and once when I release pedal.

Any ideas out there?

Thanks in advance