You may be someone who already knows the insides outs of a particular part mechanism, or you may be a mechanic by trade (and you should really know all this stuff already), or you may be merely the average Joe who wish to learn more... no dramas, let's take a refreshing look at what is a starter motor solenoid and how it works.

Basically, a starter solenoid (or also called starter relay) is that component in any car which switches a large electric current to the starter motor from the car battery, in response to small control current from the ignition switch, and which in turn sets the engine in motion. Its the same principle of a transistor, but using an electromagnetic solenoid rather than semiconductor to perform the switching. In many vehicles, the solenoid also engages the starter pinion with the ring gear of the engine.

All modern starters rely on the solenoid to engage the starter drive with the ring gear of the flywheel. When the solenoid is energised, it operates a plunger or lever which forces the pinion into mesh with the ring gear. The pinion incorporates a one-way clutch so that when the engine starts and runs it will not attempt to drive the starter motor at excessive RPM.

Some older starter designs, such as the Bendix drive, used the rotational inertia of the pinion to force it along a helical groove cut into the starter drive-shaft, and thus no mechanical linkage with the solenoid was required.

The starter solenoid is a "needy" individual and just like any human struggling to perform any actions if they are starving, a starter solenoid that receives insufficient power from the battery, won't be able obviously to start the motor and will let us know that by producing a rapid clicking sound. Yes.. that not so joyful clicking sound you heard in the morning at least once in your life just before going to work or worst by letting you down in the most unappropriates places and situations.

There are many reasons when that happens though, a low battery, corroded or loose connections in the battery cable, damaged positive red cables from the battery and a few more. The result of all these events is not enough power will be sent to the solenoid that can only push the engagement gear, making the metallic click sound.

There is a trick to know if your starter solenoid is bad.
1) Turn the ignition key to the “On” position.
2) Look for the large terminal posts on the solenoid where the thick red wires connect to the solenoid
3) Touch the metal shaft of a screwdriver to both of the large terminals at the same time.

If the engine turns over and starts, the solenoid is bad and should be replaced.

There is hope though and if you ever get stuck in remote locations try some of the tips given by our good friend MadMatt on his 80 series Landcruiser. Check it out!

You can get to these type of starters shown in MadMatt video, and if stuck you can still jumpstart off the second terminal of the starter. But other types of starters use a plunger to push on a lever to engage the drive gear so they will only turn the motor if you jump power to the motor cable but will not turn the engine over. So in these models, the solenoid can't really be serviced and needs to be replaced.
If that's the case we have got a good range of starter motor solenoid in store and if your vehicle is not listed, let us know, and we'll supply for you.