Ford 4-Terminal Starter Relay Wiring Diagram - S & I Terminals, Coil & Starter

This is an illustrated wiring diagram showing how a Ford 4-terminal starter relay (fender-mounted solenoid) connects into the starting and ignition system. The diagram uses photographs of the actual components: the starter relay, the ignition coil, and the starter motor with its integral starter solenoid. Callouts identify each connection: the battery cable attaches to one large post of the starter relay, and a cable runs from the other large post to the starter motor. The relay's S terminal receives a wire from the ignition switch that is "hot" in the Start position, while the I terminal feeds the ignition coil's + terminal (a circuit that is also fed from the ignition switch "hot" in the Run position). The starter relay coil is grounded through its mounting tab, and the starter motor is grounded via the engine block ground to the chassis. The diagram clarifies the difference between the fender-mounted starter relay and the starter solenoid, noting the solenoid is integral to the starter motor. It is useful for wiring or troubleshooting a starter relay, identifying the S and I terminals, and understanding how the I terminal provides voltage to the coil during cranking.