The park/neutral position switch is located on the automatic transaxle housing.
Manual transaxles do not use park/neutral switches. The switch provides an input to the PCM to indicate whether the automatic transaxle is in Park/Neutral, or a drive gear selection. This input is used to determine idle speed (varying with gear selection) and ignition timing advance. The park/neutral input is also used to cancel vehicle speed control. The park/neutral switch is sometimes referred to as the neutral safety switch.
The PCM delivers 8.5 volts to the center terminal of the Park/Neutral switch. When the gearshift lever is moved to either the Park or the Neutral position, the PCM receives a ground signal from the Park/Neutral switch. With the shift lever positioned in Drive or Reverse, the Park/Neutral switch contacts open, causing the signal to the PCM to go high.