94 PA, Dash Brake Light on, feels like no power assist

Wife was coming home yesterday and the brake light on the dash came on, and the pedal lost all power assist from the booster. I have great vacume running into the booster, but still the brake light is on and no assist. Also the truck pop button quit working, not sure if its related. I checked all the fuses under the dash and hood, everything looks good. I put a master cylinder on it about 2 years ago. This just came out of the blue. It worked fine, she stoped at the gas station, turned it back on and the light came on. Any ideas????

Have you checked the level of brake fluid in the reservoir?

Make sure the emergency brake isn't on slightly. This will also set the light on. Otherwise, I'd assume a bad power booster. Check to make sure the nuts on the underside of the dash driver side are tight on the inside bolts of the power booster that go through the firewall. These coming loose were a recall on some of the PA's.