A strategy is presented for diagnosing heavy vehicle electrical systems, today and into the future. The realities of diagnosing modern electronic systems are explored. In the future, original equipment manufacturers (OEM's) will hold an increasing responsibility in aiding the mechanic during the repair process. Electronic diagnostic capabilities are investigated from basic to futuristic concepts.The strategy is provided to guide the OEM and “black box” vendors through a diagnostic evolution. Diagnostic aids for today's vehicles should be realistic and compatible with systems already in place. A gradual evolution toward more sophisticated diagnostics in future vehicle electrical systems will follow.