Ford EEC-IV Self-Test Connector Diagram - STO, STI, SIGRTN & Fuel Pump Pins

This document is a labeled diagram of the Ford EEC-IV diagnostic Self-Test connector (STO) and the separate single-pin Self-Test Input (STI) connector. The larger multi-cavity connector is drawn in gray with four highlighted (red) pin positions identified by callouts: SIGRTN (Signal Return), which corresponds to EEC Pin #46; STO/CEL (Self-Test Output / Check Engine Lamp), corresponding to EEC Pin #17; and the Fuel Pump test pin, corresponding to EEC Pin #22. To the right, a small separate single-pin connector is shown and labeled STI, corresponding to EEC Pin #48. Red lines connect each callout label to its physical pin location in the connector body, allowing a reader to locate each diagnostic circuit terminal. This diagram is useful for anyone pulling diagnostic trouble codes from a Ford EEC-IV engine control system, jumpering STI to SIGRTN to initiate self-test, monitoring the STO/CEL output for code flashes, or activating the fuel pump for testing via the fuel pump pin. No year, model, part numbers, wire colors, or additional text appear in the image; applicability to the uploader's 1990 Ford Bronco is a claim not stated in the document itself.