Mechanics

Neutral Safety Switch

An important car electrical component is the neutral safety switch. This switch disables the starter operation when the vehicles transmission is not in neutral or park. If the engine was allowed to start in gear the car would immediately begin to move once the engine started. Neutral safety switches are equipped on automatic transmission vehicles only. A standard transmission car utilizes and clutch safety switch in place of a neutral safety switch. On most vehicles the reverse light function is integrated into the neutral safety switch. 

The location of the switch can vary; designs can include a transmission selector shaft or steering column mounting location. A neutral safety switch carries starter solenoid voltage when the ignition key is turned to the start position. This switch works the same way a normal switch would work except the neutral safety switch is controlled when the vehicle gear selector is moved throughout its range from park to 1st or low gear. When a neutral safety switch fails the starter or reverse lights will not operate.

Neutral Safety Switch
Neutral Safety Switch (appearance will vary)

Testing Neutral Safety Switch

Required Tools:

Test Procedure

  • Locate the neutral safety switch
  • Disconnect the wiring connector at the switch
  • Using a test light or volt-meter test for power at the wiring harness with the key in the "engine crank" or the gear shifter in the "reverse" position. (do not start the engine)
  • If power exists reconnect the neutral safety switch and probe outgoing wires at the connector.
  • If no outgoing power is present the switch has failed and needs to be replaced.
Tip : If the engine will not crank over with the car in "park" push down the brake pedal and try cranking the engine over with the car in "neutral". What you are doing is bypassing the "park" position in the switch and now are using the little used neutral circuit. If in neutral the engine starts the switch is probably bad.

Tip: Sometimes a neutral safety switch can become misadjusted. This switch adjustment can change due to normal wear of mechanism that controls switch slider.

Other complications can occur if there is a loose connection somewhere in the system. While this condition is not a shorted circuit problem, it is a condition that simply breaks the flow of electricity intermittently. To troubleshoot this problem consult a repair manual to locate the wiring schematic for your car. Repair the broken or shorted connection as needed and recheck system. Electrical problems are less complicated when the proper information is available. If further technical assistance is needed, ask our team of certified car repair technicians.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-21)