Ford 4-Terminal Starter Solenoid Wiring Diagram - S & I Terminal Functions

This document is an annotated photograph explaining how to wire a Ford 4-terminal starter solenoid (starter relay). The image shows the fender-mounted solenoid with callouts identifying each connection point. The large post on the left connects to the battery and other existing power connections; the large post on the right connects to the starter. Between them are two small terminals labeled "S" and "I". The "S" terminal is the "Start" terminal: the ignition switch sends power to it to activate the solenoid, which then sends power through the internal contacts to the starter. The "I" terminal is used on vehicles with a resistor in the primary power circuit to the ignition coil; it momentarily supplies a full 12 volts to the coil during cranking to help start the engine, and it is noted that this terminal is not used on some vehicles. A red wire is drawn from the battery post to the "S" terminal area for illustration. The diagram also stresses that both sides of the solenoid's mounting bracket must be well secured and clean, since the solenoid grounds through its mounting bracket. No year, model, or part number information appears in the document.