Manufacturers part numbers will be required to locate Starter motor solenoid, cap, or contact set
Minimum order value of £12 applies for starter components.

Starter Motor Solenoid function

The starter motor solenoid contains a solenoid coil, plunger and switch contact set.
The starter motor solenoid is an electromagnetic switch.
Power is applied to coil windings at terminal 50 when the ignition switch or starter button is in the starter crank position. The solenoid windings create a magnetic field which causes the solenoid plunger to move against switch contacts. When switch contacts close a circuit is made between B+ positive lead terminal contact and contact at terminal to motor lead. This allows electrical current to flow from the vehicle battery to the starter motor.

Starter motor solenoid failure

When a starter motor solenoid fails a click or clicking noise is often heard as the ignition key is turned but the starter motor does not rotate.

1. Check battery voltage : Meter should read 12.5v on a 12v system, low battery voltage will cause the solenoid to make a clicking sound.

2. Check main line voltage at starter solenoid B+ terminal. Low voltage can be caused by high resistance due to corroded or loose battery terminals, battery cable deterioration, or corroded terminal connections.

3. Check voltage at solenoid terminal 50 when ignition key is operated, should read as battery voltage. Low voltage at terminal 50 can be caused by low starter battery voltage, deteriorated ignition switch or starter relay contacts,

4. Check voltage at motor terminal side of solenoid with key operated, should not be greater than 0.5v difference to check (2.), if so this may indicate worn or dirty switch terminal contacts causing starter motor to run slow or not operate at all.

5. Check starter motor or engine chassis earth lead. Some systems may be insulated earth return.

Starter Motor Solenoid Types

Pre-engaged starter motor types have the solenoid bolted to the casing of the starter motor, or accessible by removal of a cover plate.

Classic and vintage vehicles may use a seperate starter solenoid bolted to the bulkhead or elsewhere in the vehicle.

Commercial vehicle heavy duty starter motors eg C.A.V. CA45 may have the solenoid fitted inside the starter motor casing

Starter Motor Solenoid Repair

In some cases it is possible to repair an original equipment pre engaged starter motor solenoid. The solenoid cap has to be unsoldered, then seperated from the solenoid canister to access terminal contact set.

Seperation of solenoid cap from canister often requires specialist tools and workshop press. We can supply a specialist tool kit for pre-engaged starter motor solenoid repair or may be able to repair your existing solenoid. Please enquire.

Starter Motor Diagnostic Help Page Link

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