- the battery is faulty;
- open circuit between ignition switch, traction relay, battery and starter;
- traction relay is faulty;
- mechanical or electrical defect of the starter.
To check the battery, turn on the headlights. If they dim after a few seconds, the battery is discharged. Recharge or replace the battery. If the headlights do not dim, turn on the starter and watch the headlights. If they dim, then voltage is reaching the starter and the fault is in it. If the headlights continue to burn brightly (and there is no click of the starter traction relay) this indicates that there is a fault in the electrical circuit or the traction relay is faulty. If the starter rotates slowly and the battery is in good condition, this indicates that the starter is faulty or there is significant resistance in the electrical circuit of the starter. The contacts of the traction relay can be checked by connecting a voltmeter between the contact of the traction relay connected to the starter and ground. When the ignition key is turned to the "engine start" position, the voltmeter should show voltage. If there is no voltage, the solenoid of the traction relay is faulty or the contacts of the traction relay are burnt. If the electrical circuit and the traction relay are in good condition, then the starter is faulty.
If damage to the electrical circuit is suspected, disconnect the battery and clean all connections and contacts in the starter supply circuit. Reconnect the battery and, using a voltmeter, check the voltage across the electrical circuit elements to the starter.
If the battery and electrical circuit are in good condition, remove the power wire from the traction relay and connect a voltmeter to it. Turn the ignition key to the "engine start" position. In this position, there should be full battery voltage.