Best asked in the Diesel/24v section. I'm not sure on the 3b, but I think it has a fuel cut solenoid/valve. The 2H has the EDIC ? that shuts of fuel at the injector pump I think. Guys have rigged up a cable to replace the EDIC when it dies.
a diesel wont shut down till its fuel and / or air is cut.
on my mercedes the "fuel solenoid" is actuated by vacume when you turn the key off it pulls the lever closed and shuts the fuel. also you can pop the hood and just pust the lever and it will also cut the fuel and shut off. but that is a cedes not a diesel cruiser but they all shut off by cutting the fuel.
it will never shut off until you kill the fuel. sounds to me your edic motor is no good. look near the injector pump you should see the edic motor. on mine i took it off and replaced it with a pull cable to shut it down . i still have my edic if you dont want to do that.
you can just shut the pig off my pushing the fuel cut off bracket that the edic hooks to forward.(to the frunt of the truck) that will be a little nicer on the truck. if you cant push it with the arm on it just pop it off. i drove my rig like that for 1 1/2 months after i went boating in my rig. take a bit to dry the nicknacks and doodads out.