750K case dozer brake pedal

bought a case 750K with 700 original hours. Dozer is strong and pushes good. The only thing I can find that don’t work is the brake pedal. The park brake on the left whenengaged stops the machine dead in its tracks. The one on the right seems to haveno effect as long as the one on the left is not engaged. I checked the 521 wire and four3.74 volts but the voltage doesn’t vary with the pedal. It reads the same no matter where the pedal is in the stroke. I had a hard code of 4331 out of range and when trying to calibrate I got err range. I thought thepotentiometer looked new but hard to say. I could see where the connector on themachine side wires had been pierced to probe them so someone been monkeying with it. I replaced the potentiometer and same result. Tried to calibrate and same message. I started to check by the manual and found two of the wires to the potentiometer plug on the machine side were crossed by checking continuity to x50 at the pcm. I swapped the wires and checked it a few more times and the continuity checks were as the manual says they should be. I now have no code but I cannot get the brake switch to calibrate. It says cal fail. I back probed the decelpotentiometer and found voltage varies on the return wire with movement of the pedal. Even when the brake switch is not mounted but plugged in it will not vary the voltage when turned. Always reads the same. I’m wondering if the new potentiometer has croaked due to someone crossing the pcm wires of maybe the pcm is shot. Any help would be greatly appreciated. Not surewhether to buy another 150 dollar sensor or try a pcm. I have a 5 volt reference at the brake switch but I think the pcmgrounds that switch. Anyone know anything about this?