To wire a 12-volt starter solenoid, first disconnect the black negative cable from the vehicle's battery, and then connect the red battery cable to the large bolt on the solenoid. If it is a remote-mounted solenoid, you must connect a control wire between the control circuit terminal on the solenoid and the car's ignition bypass terminal.
On-starter solenoids may be located on an assembly that is only accessible from under the vehicle, so lift the vehicle using a jack if necessary before beginning the process of wiring the solenoid. When connecting an on-starter solenoid, be sure to rest the solenoid somewhere convenient while wiring it, since it is heavy and awkwardly shaped, making delicate connections difficult to wire if holding the device in one hand.
After connecting the red battery cable to the solenoid bolt, connect the bypass ignition terminal wire to a small bolt under the first one. You are then ready to lower the vehicle and connect the black negative cable back to the battery. For remote-mounted solenoids, the extra cable that must be connected is typically marked with the letter "S." Closely read your vehicle's service manual to avoid accidentally wiring the wrong connections to one another.