To read a wiring diagram for a starter solenoid, follow the path of the wires shown in the diagram, and interpret where the fuses, resistors, switches and other electrical items are based on the symbols used. A starter solenoid is part of the starting system, so consult the starting system wiring diagram. A basic knowledge of how a starting system works aids in the interpretation of the wiring diagram.
It is important to remember that wiring diagrams do not show the location of parts, but rather, the circuit path. A wiring diagram does not show where the starter solenoid is, but shows how the solenoid is connected to the starting system.
In the most basic starter solenoid wiring diagrams, there is a line indicating a wire that comes out of the ignition switch and into the solenoid, sometimes labeled "relay." There is also a line that comes from the battery and into the solenoid. From the solenoid, a line extends into the starter motor, and from there into the battery. This shows that when the key is turned, activating the ignition switch, the solenoid turns on and allows the starter motor to switch on. The starter motor then engages the flywheel on the engine, and turns off when the rotations per minute are up to speed.