Troubleshooting the brake light

[Redgstang]

I have a 92 mustang gt and my brake light on the dash has been staying on.. I have checked the fluid and the brakes.. The one thing I don't understand is that the light will go off when braking a little hard instead of gradually slowing down to a stop but the light will pop back on as soon as i come to a complete stop or start to take off again.. Any ideas on what might be the problem or what to look for??