brake light on 82 LeSabre

HI--I was moving my bro's 82 in the yard, hit the brakes & the brake light came on, and when I hit the pedal it was as hard as a rock, like when you have to pull a car with no power to it....then when I touched it a few more times, the light went off and the brakes felt normal again. I haven't moved it again, but was wondering, is this something to do with the power assist or whatever it's called, cause if it was a leaky line, I know it don't do nothing like that! Any help or suggestions are greatly appreciated....he has put so much money in this car, it isn't even funny......but it's not all that many miles, but sat a long time from the person he bought it from. And he's been driving it about 2 yrs. now, I think. Thanks!