If you mean ECU (Electronic Computer Unit) Code Reader, I may be wrong but I am not sure that the early 1990 L300 had that capability/feature, and I am glad it does not
What Lapprentis said. Some later model fuel injected petrol vans had an OBD port (though it was Mitsubishi's own protocol and predates the American OBD2 standard), but I've never seen one on a Diesel.
Could you share a photo of the connector you're hoping to plug a code reader into?
Nothing says "poor workmanship" more than wrinkles in the duct tape.