brake problems

Check the fluid level in the master cylinder. Mine was really picky and liked to be completely full. I actually ended up switching to vacuum brakes yesterday however.
Don't let the motor run more than 20 seconds. You will burn it up if you do.

When the motor is running, do you see the fluid moving in the ps of the bowl? If so, you are most likely internally leaking. To confirm it, get a peice of clear vynl tubing that fits snugly in the ps rear port of the bowl and turn on the motor. If the fluid runs up the tube, you are internally leaking and it's time for a new P/M.

If you find it is NOT internally leaking, I can only guesses from my keyboard that the relay is fused closed and not shutting off the motor. The pressure switch could be bad also. Only way to test it is with a known good one or a new one.