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Starter (Ignition) Relay

The Starter Relay is a device that utilizes a small amount of electrical current from the ignition switch to energize an electromagnet that operates a larger current carrying switch, which in turn triggers the operation of the Starter Motor or Starter Solenoid.

The starter for a combustion engine is nothing more that an electric motor with a gear. It turns the engine by the flywheel until the engine can turn under its own power. This requires a great deal of electrical current, and the tiny wires that run from the ignition switch are too small for such a load. So engineers introduced the starter relay. Here is how it works:

 

When you turn the ignition to the ‘Start’ position, a light electrical current is sent from the ignition switch to the starter relay. Since that small amount of electrical current is unable to power the starter, it instead powers a tiny electromagnet, which closes a much larger circuit. The larger circuit consists of a thick wire from the battery to the starter relay, then from the starter relay to the starter motor. In simple terms, the starter relay uses a small electrical current to activate a large electrical current.

 

Symptoms of Wear or Failure of the Starter Relay

  • Nothing happens when the key is turned to the ‘Start’ position: This is because the electromagnet has worn out, or there is corrosion on the contacts inside the relay.
  • Starter relay clicks, but the engine does not crank: Resulting from corrosion inside the relay, or a bad connection to the relay
  • The engine attempts to start without the key being turned to the ‘Start’ position: When the engine tries to start itself, but the key is not in the ‘Start’ position, the relay has likely become wet, stuck, or damaged, and should be removed from the vehicle immediately.
  • Relay does not click on starting, but functions when removed from the vehicle: The underhood power center is likely damaged, preventing the relay from sending or receiving power.

Related Repair Advice for the Starter Relay

  • When turning the key to start the vehicle produces no results, the starter relay is a possible suspect, but the ignition switch may have failed as well.
  • As with all electrical systems, testing is necessary, as there is usually no physical indication of failure.
  • Disassembling and cleaning a relay can restore functionality, but they are inexpensive, so replacement is preferred. Cleaning will not always lead to a functioning relay
  • There are many types of relays, with many different applications. Making sure the relay is identical in every way will eliminate fire hazards, and ensure the relay will function as intended.
  • When the relay clicks, but the engine does not start, the starter is a strong suspect, as well as the battery cables and starter circuit. 

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