Mzdafrk

I was searching on Google and found this topic. I am not trying to thread jack the topic, this is the closest problem I have found to what I am dealing with, so I am very interested. I have been searching for weeks, and this is the same problem I am having on a 1956 Desoto. I was having a problem with the brake pedal falling to the floor, so I replaced the Master Cylinder, Bleed all 4 Drums, Flushed all the fluids, and found a leak in the booster, SO I sent it out and had it rebuilt. A few weeks later I got it back, and put it in. Then it sat for a couple weeks. I decided to drive it on a nice day, I noticed that the Pressure switch on the master cylinder, to turn the brake lights on, was activated and the brake lights were on. I tried fiddling with the switch but nothing made the lights go off. So I started up the car, and tried to move and the brakes felt very stiff. SO I figured it was time to get the car home, I was only a few miles away. When I started it back up the brakes locked up completely. I was sitting in a parking lot so I tried to move forward and backward but was not able to move. I then Borrowed a line wrench and bled the pressure off the master, everything returned to normal. So I drove the car home and parked it. I went out the other day and the brake lights were on again...?! I have been searching for similar problems, but couldn't find any until I found this thread. We are experiencing almost the same problem, and I am stumped. I have all new parts, and the brakes are locking up? New Vacuum Canister, New Master Cylinder, New Brake Booster, flushed all the fluid, bled thoroughly. Any Ideas??? All I have come up with so far is that one of the parts is defective inside the master, and is not releasing pressure, so every time I step on the brake pedal it creates more pressure until it eventually locks up. But I question that theory simply because that doesn't seem right. I am open to trying different things to try and fix it, and will give any updates when I figure something out.