will not start and run if tbi unit plugged in on 1990 Dodge Ram 50

i cannt find the diagonis plug on this truck anywhere and i have replaced fuel pump/regulator/tbi unit /mass air flow /coil and the engine will not run with tbi unit plugged in it is a import it has the 3.0 misabushi engine 4x4 5speed

Asked by for the 1990 Dodge Ram 50
The Diagnostic plug is in the Engine Compartment and it is Black. You need to have the system scanned before you so pend more time and money just trying parts.

try here for some info on how to get the codes out of your Truck