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The start signal from the ignition switch during Starter motor test

The start signal from the ignition switch during Starter motor test

The circuit labeled by the number 2 in the photo is commonly known as the S terminal of the starter Solenoid. Attached to this S Terminal is the wire that comes from the ignition switch via the Neutral Safety Switch. This is a 12 Volt Signal.

When the key is turned to crank the engine, juice flows from the ignition switch, thru' the Neutral Safety Switch and onto the S terminal of the starter Solenoid.
 
 

On a good and working starter motor, as soon as this 12 Volt Signal is received, the starter motor comes alive and cranks the engine.

This test verifies the presence of these 12 Volts and indirectly tests the Ignition Switch and the Neutral Safety Switch. You'll only get one of two results from this test: you'll either get 12 Volts or not. Let's get started:
Step 1:
Raise and support the vehicle on jack stands (if applicable).
The starter motor must remain connected to all of its cables/wires.

Step 2:
Attach the BLACK multimeter lead (with an appropriate tool) to the Negative Terminal of the battery.
With a wire-piercing probe or a suitable tool, pierce the wire that is attached to the S terminal of the starter Solenoid
Or if you have enough room, touch the S terminal with the multimeter lead.

Step 3:
Put the multimeter in Volts DC mode.
Have an assistant turn the key to the Start Position and have him or her hold it there while you observe the multimeter's voltage reading.
If when your assistant turned the key to the Start position to crank the engine (and kept it there), and if the multimeter:
  1.DID NOT register any voltage, then the starter motor is not the cause of the Does Not Crank condition. Without these 12 Volts here (when the key is turned to the Start position) the starter motor will not come out to play. Possible causes for this missing voltage are:
    Bad Ignition Switch.
    Bad Neutral Safety Switch.
    Go to the test: Adding 12 Volts to the S Terminal Circuit.
  2.DID register 10 to 12 Volts, then the Start Signal is being received. The presence of this voltage confirms that:
    The Ignition Switch is good.
    The Neutral Safety Switch is good.

The next step is to make sure the starter motor is getting plenty of Power. For this test, go to the test: Voltage Drop Testing the Power Circuit.

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