The starter motor is the most important electrical component on a scooter. It engages the ring gear mounted to the flywheel, which cranks the engine. As a result of this, it’s essential to keep the starter in good working order, or you could be facing a huge repair bill.

There are two main circuits that connect to a starter motor: The high current circuit and the low current circuit. The high current circuit is made up of thick wires that run from the battery to the positive battery terminal and the starter relay, whilst the low current circuit uses smaller wires.

The high current circuit carries the very high current needed to turn the engine over. This circuit is made up of the 6 to 8 gauge wires that connect the positive battery terminal to the starter relay, and the heavy gauge wires which run from the relay to the starter motor.

When a starter relay is activated an electromagnetic field closes the high current contacts and completes the high current circuit, and when the low current circuit is opened it opens the high current contacts again to enable the start motor to operate. This is all controlled by a starter solenoid (normally brown on Piaggio scooters) and can be operated either through a starter button or a brake light switch.

Once the solenoid is opened there are a number of tests that you can perform to ensure the starter solenoid is functioning correctly.

Firstly you need to make sure that the thin black wire which runs to the starter relay is permanently connected to earth. This will be found on the back of the moped, sometimes behind the left hand rear panel.

If this wire is not connected to earth then the starter relay will not work properly and should be replaced.

In some cases it is possible to remove the starter solenoid without removing the relay. This is usually the case with simple models, but more complicated models will require the relay to be removed. You can consult your Haynes manual for this, as some models are relatively easy to remove and others will require spanners or even a fuse change!

You’ll also need to disconnect the green/black wire from the starter relay. This is usually located near the battery -ve terminal and will be marked with a green stripe or some other marking.

Next, reconnect the green/black wire from the starter relay to a test bulb and leave one side of the bulb disconnected. If the bulb glows when you pull the brake lever and press the starter button this means that the low current circuit is operating correctly. If the bulb does not glow when you pull the brake lever and press the button this indicates that the starter relay is faulty and should be replaced.

Once you have tested the high and low current circuits then you can decide if the starter solenoid is faulty or not. If the starter solenoid is faulty then you will need to replace it as soon as possible!