Page 8 - august newsletter

August 2020
www.tswfl.org
`Triumphs Live On
Tech Corner
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-continued
motor terminals. The battery terminal is the one referred to above (the big bolt with all the brown wires of varying thicknesses). The starter motor terminal is the other big bolt through the solenoid end cap attached to a such that the top metal strap that comes out of the side of the starter motor. Note that this terminal has no other wires attached to it!
Inside the solenoid, these bolts are attached to individual contacts that are isolated one from the other. The solenoid, when activated, bridges these contacts, thus connecting the starter motor directly to the battery and making the starter run. When the key is turned to start the plunger, as it is drawn into the solenoid, it simultaneously pulls a lever that makes the starter pinion gear thrust out and engage the ring gear on the flywheel, turning the engine and starting the car. When the ignition key is released, the ignition switch returns to the run position, which allows the car to run but which cuts current to the starter solenoid, resulting in the withdrawal of the pinion gear from the flywheel and deactivating the starter motor.
Similar to the starter relay, the solenoid uses an electromagnet to complete a circuit. When electrical current from the switch enters the solenoid, it energizes a small electromagnet inside the solenoid. This electromagnet pulls on a metal arm attached to the battery's positive terminal against a metal plate attached to the starter terminal. In this way, the starter solenoid mimics the behavior of the ignition switch; you can think of the starter solenoid as a second ignition switch that sits in line between the battery and the starter.
The sound of the metal arm being drawn down to the metal plate is the clicking sound you hear when turning the ignition key. If your battery and charging system are good but the engine won’t crank click you hear a sharp click when you turn the key to start. You’re probably hearing your starter solenoid pulling in the plunger. The starter relay also makes a slight click, but not enough to confuse it with the louder sound of the starter solenoid. A loud click is no guarantee that the starter solenoid is working properly, though, so I would check it and the starter motor first. Usually, hearing this sound means the solenoid is operating correctly. If no sound is heard, then further testing is necessary to eliminate the solenoid as a problem. Here are the simple tests for checking the solenoid:
Connect a test light to the output terminal of the solenoid. There are two small terminals sticking out of the face of a starter solenoid. One is the 12-volt positive (top) that comes from the battery. When the starter solenoid is activated, it connects the lower terminal to the upper one internally, engaging the starter motor.
1. There should be continuous power going to the top solenoid terminal.
2. Press the red lead from the test light onto the top terminal and hold it in place.