F 150 2WD Pickup V8-5.4L SOHC VIN 3 (1999)
Starter Relay: Description and Operation
Automatic Transmission
The starter motor solenoid relay switch:
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controls current to the starter solenoid.
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is engaged by the ignition switch.
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connects the battery to the starter motor.
The digital TR sensor prevents starter motor engagement unless the transmission is in the NEUTRAL or PARK position.