Neutral Safety Switch

Center terminal of the 3 terminal neutral starting and back-up light switch provides ground for starter solenoid circuit through shift selector lever in "PARK" or "NEUTRAL" positions only.
To test, remove wiring connector from switch and check for continuity between center pin of switch and case. Continuity should exist only when transmission is in "PARK" or "NEUTRAL".
NOTE: Check shift linkage adjustment before replacing a switch which tests bad.
To replace, unscrew switch from case (some fluid will escape). Move shift selector lever to "PARK" and then to "NEUTRAL" position. Check to see that switch operating fingers are centered in switch opening in case.
Install switch with new seal into case and tighten. Check transmission fluid level. The back-up light switch circuit is through the 2 outside terminals of the switch.
Continuity should exist between the two terminals only when transmission is in reverse. No continuity should exist from either terminal to case.

Fig 1: Neutral Safety and Back-Up Light Switch

Center terminal for neutral safety; side terminals, back-up circuit.