Brakes locking; phantom gripe

[Second Shadow]

I have a 93' 240sx se(four wheel disk), manual trans, without ABS. Recently my brake light was mess up and stayed on all the time. it was just the plug in the brake pedel that touches the switch so I plugged it with a bolt and now it works fine. However now, after about 10 to 15 minutes of driving, the brakes slowly start to engage on their own, and about 3 minutes after that they are lock so hard the car won't move. The pedel has a little slop at first but as soon as the brakes start to lock, it gets hard as a rock. if I pull the vacuum line off the booster they unlock and work but the booster doen't and the pedel is still as hard as a rock and it takes A LOT of force on the pedel to get them to work at all. However, if pull and then reconnect the vacuum line they start to work again for another couple of miles, then lock up again. I've already changed out the booster and master cylinder, and bled the system quite extensively. I checked the vacuum check valve and it seems to be working fine. I don't think it's the calipers because once the locking starts they all do it at the same time but work fine before that, and then work again once you pull&reattach the vacuum hose. I've even removed the bolts that pluged the holes in my brake pedal just in case they were messing up the adjustment, didn't help. Does anybody have any Ideas?