I would urge you not to start replacing parts! Electrical problems are not an area where guesswork works best. TROUBLESHOOT the problem, using established proceedures that are well documented in MANY places. The charging system on your diesel is not special, and is the same as most any other Ford of that era, as well as many other makes of cars and trucks. You NEED to buy a volt/ohm meter. NOT PARTS. At least not right yet.