Something isn't releasing (heavy use) or the switch needs to be reset.
Has it been this way since the brake job? Can you take it back?
Not releasing: Could be an ABS valve (unlikely) or the caliper pins weren't cleaned and lubed properly or a stuck piston. Vehicle info would help a lot.
Switch reset: Where the single wire plugs into the master cylinder (or a little block attached to it), unhook the wire, unscrew and remove the switch. Screw it back in to reset and hook the wire back up.