Where is the control module in an 1988 fifth ave?

Taking a guess, Your 1988 5th Ave has a 318ci motor with Lean-Burn Engine control. Chrysler put the control module in the rectangle box attached to the side of the air cleaner. All of the engine control module is inside that box to include the transistorized ignition system. Your distributor will have two pickup coils in it and not have a vacumn advance located on the side of it which will be another way of telling if you have the Lean-Burn system.