All types of vehicles and equipment
Starter solenoids are intended for starting circuits only. Do not use for high amperage continuous duty applications. This bulletin will explain common automotive type starter solenoids and how they work.
Technical Services receives many calls on the installation of starter solenoids and the various use’s that they are believed to be adapted to. The starter solenoid is a relay that serves as an electric switch for the starter of an engine. The solenoid takes voltage from the battery on one large terminal, and when commanded by the ignition switch, connects internally to allow power to travel through to the other large terminal sending voltage to the starter.
Installation of the solenoid can sometimes be confusing. When replacing your inoperative solenoid try to take a picture of the orientation of the wire leads or draw a diagram of the wires, where they come from and where they are going. This should make your installation a breeze. If that opportunity has slipped by the remainder of this article should guide you through your installation.
Most common automotive starter solenoids have 4 threaded posts, two that are larger and two that are smaller. The base of the solenoid serves as the ground for the solenoid, the solenoid must be mounted down in order to work. One large wire goes to the battery positive post. The other large wire goes to the starter motor. The two smaller posts are marked with an “S” and an “I”. The “S” post is for start. When commanded by the ignition switch voltage is applied to the “S” post creating the magnetic force to internally connect the two large posts and allow the higher current to pass through to the starter. The “I” stands for “ignition” and is commonly used for powering your vehicles primary ignition system during the cranking mode. Not all applications will use this terminal. Battery voltage is supplied to the ignition coil or ignition control module during the engine cranking mode to increase the voltage during start up. When the ignition switch is released from the cranking mode the voltage to the “S” and “I” posts are no longer supplied.
Proper installation of the starter solenoid will ensure trouble free operation. As with any vehicle repair consult your vehicle manufactures repair guide prior to attempting any vehicle maintenance.