When you turn the important to begin your van, it may seem as whether the ignition switch opens the starter circuit.The starter solenoid is basically a large relay located either right on the starter or in another location. A relay is a part that uses a small amount of current to control another circuit that typically uses a much larger amount of current. A failure of the starter solenoid will result in an inability to start the car (unless the car has manual transmission and the clutch can be "popped" while the car is rolling down a hill or is being pushed).
But what's really happening is that the ignition switch activates the starter solenoid. In some cases, if you can't start your car, it's because the starter solenoid has malfunctioned.
Facts
Function
Starter solenoids may have up to three functions. All starter solenoids are responsible for closing the circuit between the battery and the starter. Some will move the starter pinion gear to mesh with the teeth on the flywheel ring gear. Some are used to bypass the resistance wire, if any, that may be found in the ignition circuit.
How it Works
Inside a starter solenoid is a plunger surrounded by a coil, or windings. When the ignition key is turned to the start position, a small amount of current is passed through the coil. This creates a magnetic field, which pulls the plunger inward. At one end of the plunger is a metal disc, which touches two terminals. These are connected to the battery and the starter; thus, a large amount of current is delivered to the starter.
Types
There are basically two types of starter solenoids. One is attached to the starter, and not only opens the starter circuit when the plunger moves, but also moves the starter pinion gear into position to turn the flywheel which turns the crankshaft to start the engine. The other type, which may be located on a body panel, only serves to open the starter circuit.
Benefits
Because the starter draws such a large current (500 or more amps), the wires that carry that load must be of a large size. The starter solenoid allows the wires that lead to the ignition switch to be much smaller, thus making it much easier to place the ignition switch on the steering column (or dashboard). Building a car without the starter solenoid would be more expensive because of the need to route heavy wires to the ignition switch.
