Ford Mustang Service Manual: Relay Switch

Starting System (Description and Operation)

Starter Motor

The starter motor is a 12-volt unit that has the starter solenoid mounted on the drive end housing and functions as follows:

  • The current flows through the solenoid energizing coil until the solenoid plunger is at the end of its travel.
  • The plunger closes a set of contacts that bypass the energizing coil, letting the holding coil keep the starter drive engaged and passing starting current to the starter motor.
  • The motor is energized when the starter solenoid contacts are closed.
  • The starter drive engages the flywheel ring gear and starts the engine.
  • An overrunning clutch in the starter drive protects the starter motor from excessive speed when the engine starts.

Starter Relay

The starter interrupt relay consists of:

  • pull in coil and contacts
  • When the ignition switch is in the START position:
  • the pull-in coil is activated and pulls the contacts together.
  • current passes through the starter relay from the engine compartment power distribution box to the starter solenoid.

Clutch Pedal Position (CPP) Switch

The CPP switch for:

  • a manual transmission closes when the clutch pedal is depressed, completing the starting circuit.
  • an automatic transmission is a jumper inserted in place of the CPP switch to complete the circuit.

Starter System - Operation

When the ignition switch is turned to the START position the starter relay switches power to the starter solenoid causing the starter motor to engage as long as:

  • the clutch pedal is depressed (manual transmission only).
  • the digital transmission range (TR) sensor is in PARK or NEUTRAL (automatic transmission only).
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