Ford EEC-IV to MegaSquirt Piggyback Wiring Diagram - Adaptor Board Layout

This document is a hand-drawn block diagram illustrating how to connect a MegaSquirt aftermarket engine management system in a 'piggyback' arrangement alongside a stock Ford EEC-IV engine computer. The diagram shows six main elements and their interconnections: the factory Ford EEC-IV module connects to a 'Salvage EEC connector and Harness,' which routes into an 'EEC adaptor board' via a DB25 connector. The adaptor board also plugs into the 'Stock Ford EEC Connector,' which ties into the 'Stock Engine Harness.' On the MegaSquirt side, a 'Megasquirt DB37 to DB37 jumper cable' links the MegaSquirt unit's DB37 port to a DB37 connector on the EEC adaptor board. The reader learns the overall wiring topology: the adaptor board sits between the vehicle's stock engine harness/EEC connector and both computers, using a DB25 connection toward the salvage EEC harness/EEC-IV and a DB37 connection toward the MegaSquirt. No pinouts, wire colors, part numbers, fuse values, or year/model applicability are stated; the diagram conveys only the high-level cabling arrangement for interfacing the two ECUs. It was uploaded to a 1991 Ford Bronco gallery, consistent with EEC-IV usage, though the document itself does not state a vehicle.