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

This document is an annotated photograph explaining the wiring of a Ford 4-terminal starter solenoid (starter relay). The image shows the solenoid mounted on its bracket with callouts identifying each connection point. The left large stud connects to the battery and other existing power connections, while the right large stud connects to the starter. Two small front terminals are labeled "S" and "I": the "S" (Start) terminal receives power from the ignition switch to activate the solenoid, closing the contacts to send power to the starter. The "I" terminal is used on vehicles with a resistor in the primary power circuit to the ignition coil; during cranking it momentarily supplies a full 12 volts to the coil to aid starting, though it is not used on some vehicles. The document also stresses that both sides of the solenoid's mounting bracket must be well secured and clean, since the bracket provides the ground path for the solenoid. A reader can learn which wire goes to which terminal, the purpose of the S and I terminals, and the importance of proper grounding through the mounting bracket. No specific year, model, or part numbers are stated.