[V30crewcab]

sounds like its not getting the trigger from the starter wire. its wired exactly like a cummins truck, a ground, the pull wire, and the hold wire. when you hit the key to power the starter, it sends power to the strong pull part of the solenoid. theres a smaller part of the solenoid that holds it in as long as the key is on. mine was kicking off when I hit a bump or something as well. I had to take the end off the shutdown lever, energize the solenoid to the run position, and bend the lever so it lined up in the full on position. it was bent so the solenoid couldn't move in all the way, and it would let loose easily.
I know everyone likes the simplicity of the cable, but I like mine working with the key like it was built. I had a cable on my chevy truck with a cummins when I first built it, then I got in a wreck, shut the key off and the engine didn't quit. took me a few seconds to realize I had to pull the cable. decided it was a safety hazard to have it that way so bought the right part and fixed it.