Closed loop firing system is the combination of circuits that must work at all times with the computer in order for the ignition to release fire to the cylnders. Interupt the wrong wiring loop and the truck won't run. I have seen this to include door opening sensors, brake safety switch's, as well as fuel pressure switch's.
Chrysler changed a lot of their systems with the introduction of the V-10, and has changed them again every 3 years or so "trying" to improve on the "bugs"
I am sure that you can get this from Dodge for your model.
Good Luck