89 mustang OBD-II?

The EEC-IV has a diagnostic port located in the rear of the driver's side engine bay. It consists of a trapazoidal-shaped connector and a small single-pin connector. This can be plugged into any $20 EEC-IV code reader.

However, EEC-IV is not capable of delivering real-time data, or as complete diagnostics as the OBD-II systems.