The Brake Pedal Position (BPP) switch is two switches in one. There should be 5 wires coming from it. One switch is a single pole that operates the brake lights. The other is a double pole that sends a signal to the PCM (and cruise control module if you have one) to do things like break the cruise control, allow 4WL operation, etc.

I just replaced mine recently because it was doing exacly what yours is. Once I replaced it, an extremely light tap disengages the cruise. It's cheap and easy to replace.

Ford Part #F87Z13480AA. $13.44+shipping from Ed the Parts Guy (www.ftepartsguy.com). Or $24.89 MSRP from your local dealer.