Brake pedal to the floor
 

Just picked up a 72 D100 Saturday morning, had no issues transporting it on to the trailer and off the trailer and driving it up into my driveway. Been moving it around in the driveway and working on a few things. I adjusted the rear drums and haven't done the front yet. But last night I noticed after a few pumps the pedal sinks to the floor and the light comes on. I checked all the wheel cylinders and traced all the brake lines, No leaks and the reservoir was topped off. So is it possible the Master Cylinder died on me after being used so much after the truck sat for 2 years before I bought it. Thanks in Advance guys.

It's very possible that the master and every wheel cylinder needs to be replaced after sitting.

Yeah I just ordered a new Master Cylinder and all new Wheel Cylinders, and been soaking them down with PB Blaster, everything should be in Thursday from RockAuto.

Good job, fix it once and be done.