94 merc grandmarkee wont go into park wont start will start if you wiggle in nutral

Park neutral safety switch could be bad , also the shift interlock safety system .
Shift Interlock System A brake/shifter interlock system consists of the following:

• ignition switch (11572)
• brake pedal stoplight switch (13480)
• brake shift interlock module
• brake shift interlock solenoid assembly (attached to key interlock assembly)
• necessary wiring

On floor-shift vehicles, the ignition/shifter interlock cable (3F719):

• locks the floor shift transaxle range selector lever in the PARK position when the ignition switch is in the LOCK position.
• requires the floor shift transaxle range selector lever to be in the PARK position to turn the ignition switch to the LOCK position.

Condition Possible Source Action

• Shift Interlock System Does Not Release or Lock Properly

• Circuitry open/shorted.
• Blown fuse.
• Damaged stoplight switch.
• Damaged shift lock actuator.

• GO to Pinpoint Test A .

PINPOINT TEST A: SHIFT INTERLOCK SYSTEM DOES NOT RELEASE OR LOCK PROPERLY A1 CHECK ELECTRON IGN FUSE

• Check Fuse 5 (5A) located in fuse junction panel.

Is fuse OK?
Yes No GO to A3 . GO to A2 . A2 CHECK FOR SHORT TO GROUND

• Turn ignition switch OFF.
• Remove Fuse 5 (5A).
• Disconnect shift-lock actuator connector C203 located to the right of steering column.
• Measure resistance of the Circuit 1003 (GY/Y) between the correct terminal of Fuse 5 (5A) and ground.

Is resistance greater than 10,000 ohms?
Yes No REPLACE Fuse 5 (5A). GO to A3 . SERVICE Circuit 1003 (GY/Y) wire between fuse junction panel and shift-lock actuator. A3 CHECK POWER SUPPLY FROM FUSE 5 (5A)

• Reinstall Fuse 5 (5A).
• Turn ignition switch to RUN.
• Measure voltage on Circuit 1003 (GY/Y) wire and ground.

Is voltage greater than 10 volts?
Yes No GO to A4 . SERVICE Circuit 1003 (GY/Y) wire between interior fuse panel and shift-lock actuator. A4 CHECK POWER SUPPLY FROM FUSE 28 (15A)

• Turn ignition switch OFF.
• Disconnect connector C2016.
• Turn ignition switch ON.
• Measure voltage on Circuit 10 (LG/R) and ground.

Is voltage B+?
Yes No GO to A5 . SERVICE Circuit 10 (LG/R) for open. RESTORE vehicle and RETEST system. A5 CHECK WIRE BETWEEN STOPLIGHT SWITCH AND SHIFT-LOCK ACTUATOR

• Turn ignition switch OFF.
• Disconnect shift-lock actuator connector C203.
• Apply brake pedal.
• Measure voltage on Circuit 810 (R/LG) wire and ground.

Is voltage greater than 10 volts with brake pedal applied and less than 1 volt with brake pedal released?
Yes No GO to A6 . SERVICE Circuit 810 (R/LG) wire between stoplight switch and shift-lock actuator. A6 CHECK SHIFT-LOCK ACTUATOR GROUND

• Measure resistance of Circuit 57 (BK) and ground.

Is resistance less than 5 ohms?
Yes No REPLACE shift-lock actuator. SERVICE BK wire.