Transmission Shift Interlock 93 SHO - Automatic Transmission

Frank C Travanty · Aug 5, 2019

The Transmission shift Interlock solenoid seems to be hung up such that most of the time when I start the car I can't shift out of park. I suspect the interlock solenoid, but not sure. I have had the console off and looked around, but have not removed the four screws that mount the shifter assy to the frame. So, seeing anything at this point is difficult. At his point I would like to obtain a parts break down/part numbers of the components inside the metal housing, to help me understand what I'm dealing with, and possibly obtain a new part. Also to locate the solenoid. I've searched the Internet for service manuals with no practical luck. Any help or suggestions in getting a parts breakdown would be appreciated.
Been thinking of making a personal visit to the local Ford service to see if they can supply a breakout diagram/parts list.
Thanks,
Frank

luigisho · Aug 5, 2019

Since they can't get many of the parts that old anymore, they are usually pretty good about getting you a diagram. Just my random experiences. Some will give me oem part numbers for anything, and some hem and haw when they are plentiful in the supply chain and don't want me shopping around.

rubydist · Aug 6, 2019

iirc, there is not a solenoid. there is a cable that goes from the brake pedal under the heater diffuser and into the shifter. when you press on the brake pedal, it moves the cable which unlocks the shifter so it can move. I have just disconnected the cable at the shifter in the past to get around issues with this. sorry, its been long enough I don't remember exactly what it looks like at the shifter.

NoSlo · Aug 6, 2019

There is a solenoid:

The floor shift interlock system consists of a solenoid assembly attached to the key interlock assembly, a bracket retaining the solenoid, and the necessary wiring. The solenoid is energized when the ignition switch is turned to the ON position, locking the floor shifter in the PARK position. When the brake pedal is depressed and the stoplamp switch is activated, the shift lock solenoid is deactivated and the floor shifter can be moved out of the park position.

in other words:

in the ignition locked, key-removed position, the ignition switch controls the cable to block shifting;
in the ignition-on run position, the actuator solenoid being "on" blocks shifting via the cable, until you press the pedal.

If you have a failing brake lamp switch on the pedal, you won't be able to move out of park when the key is in the on position. Instead, move the key to the "off" position (turn it forward from "lock", but not on) and see if you can shift out of park. If so, you have diagnosed a problem with a brake switch - also your brake lights won't turn on. Disconnecting the battery will disable any solenoid operation.

The unlikely problems are the solenoid being stuck in the engaged position, or the ignition switch linkage or cable being misadjusted or broken.

The solenoid is in the steering column. Here's a PDF of the service manual section for steering column.

Frank C Travanty · Aug 6, 2019

NoSlo said:
There is a solenoid:

The floor shift interlock system consists of a solenoid assembly attached to the key interlock assembly, a bracket retaining the solenoid, and the necessary wiring. The solenoid is energized when the ignition switch is turned to the ON position, locking the floor shifter in the PARK position. When the brake pedal is depressed and the stoplamp switch is activated, the shift lock solenoid is deactivated and the floor shifter can be moved out of the park position.

in other words:

in the ignition locked, key-removed position, the ignition switch controls the cable to block shifting;

in the ignition-on run position, the actuator solenoid being "on" blocks shifting via the cable, until you press the pedal.

If you have a failing brake lamp switch on the pedal, you won't be able to move out of park when the key is in the on position. Instead, move the key to the "off" position (turn it forward from "lock", but not on) and see if you can shift out of park. If so, you have diagnosed a problem with a brake switch - also your brake lights won't turn on. Disconnecting the battery will disable any solenoid operation.

The unlikely problems are the solenoid being stuck in the engaged position, or the ignition switch linkage or cable being misadjusted or broken.

The solenoid is in the steering column. Here's a PDF of the service manual section for steering column.

Frank C Travanty · Aug 6, 2019

Thanks for all your expertise on the shift interlock operation. That helps. My question is with regard to the PDF file. I indicates it is for a column shift vehicle. Assume C203 is the actuator?
My 93 SHO has floor SHIFT with automatic transmission. Is the solenoid still located in the steering column?
Thanks, Frank

NoSlo · Aug 6, 2019

Frank C Travanty said:
Is the solenoid still located in the steering column?
Thanks, Frank

Yes, where it says "attached to the key interlock assembly" below. The solenoid's function is not even in doubt in any diagnostic procedures with this symptom, though. A non-functioning solenoid allows you to shift.

See if your brake lights are working.

For not releasing, the brief overview - including the button on the shifter possibly not functioning:

You see callout #2, the interlock cable, leads from the column to the shifter:

Fuse #5 powers the solenoid, while #1 provides the brake lights and signal that you are pressing.

Frank C Travanty · Aug 6, 2019

NoSlo said:
Yes, where it says "attached to the key interlock assembly" below. The solenoid's function is not even in doubt in any diagnostic procedures with this symptom, though. A non-functioning solenoid allows you to shift.

See if your brake lights are working.

For not releasing, the brief overview - including the button on the shifter possibly not functioning:

You see callout #2, the interlock cable, leads from the column to the shifter:

Fuse #5 powers the solenoid, while #1 provides the brake lights and signal that you are pressing.

The brake lights work fine. The problem is also intermittent, which makes this a bit more challenging. Can get it out of park normally part of the time.
I decided to go in the vehicle and do some tests from the drivers seat, in hopes of making sense of this.

Condition: Result:
Key in Ignition(off) Park Locked
Key moved from off (No dash lights) Can move shifter from park & thru gears by depressing handle ****
Key moved to ACC (dash lights on) Can move the shifter from park some of the time (mostly not)
Start Car Normal operation this time
Leave in Neutral Can start/stop engine but key is captive.

Like I said, this seems intermittent, so I'm going to mull this over, with the aid of your inputs. Would be nice to know what the rest of the call outs are on the parts layout.

Thanks Frank

NoSlo · Aug 6, 2019

The other stuff is the vacuum parking brake release and the cabling to the transmission range sensor on the transaxle.

You can unplug the solenoid's electrical connector inside the column and it will never activate, leaving only the remaining mechanical factors. The safety prevents toddlers and pets from shifting a running car. It does have some relay-like internal solid-state components that switch it off when the brake pedal input is detected, so that is one failure mode that may be internal to the actuator.

Frank C Travanty · Aug 6, 2019

NoSlo said:
The other stuff is the vacuum parking brake release and the cabling to the transmission range sensor on the transaxle.

You can unplug the solenoid's electrical connector inside the column and it will never activate, leaving only the remaining mechanical factors. The safety prevents toddlers and pets from shifting a running car. It does have some relay-like internal solid-state components that switch it off when the brake pedal input is detected, so that is one failure mode that may be internal to the actuator.

That"s a good input. I will save it as a last resort. I did try a couple more things. Tried moving the key from lock to "not on". This gave intermittent operation of the brake lights. When I started the car the brake lights seemed to work fine. Maybe the brake light switch. I looked around the brake pedal and there is a small metal module with connectors and leads going to the fuse area, that appears to be lined up with the brake plunger rod. Can you verify if this is the brake light switch?
Checked the text which contains the (3F719) reference , just before pinpoint test A, and that worked as described. going to look at a couple more things.

NoSlo · Aug 6, 2019

The switch is the only one that you will find operated by the brake pedal under the dash. (the redundant cruise-control cutout is a switch under the master cylinder). Disconnecting the battery or the brake switch harness connector, you can back-probe the connector or wires with a multimeter in continuity "beep" mode while pressing the pedal, but with the symptoms you've described, I'd already be replacing the switch - you don't want to get rear-ended either.

Frank C Travanty · Aug 7, 2019

NoSlo said:
The switch is the only one that you will find operated by the brake pedal under the dash. (the redundant cruise-control cutout is a switch under the master cylinder). Disconnecting the battery or the brake switch harness connector, you can back-probe the connector or wires with a multimeter in continuity "beep" mode while pressing the pedal, but with the symptoms you've described, I'd already be replacing the switch - you don't want to get rear-ended either.

Think you are correct on the switch. I removed the brake light switch cable and the system worked as described in your first post with the key in the "not on" position consistently. I banged the switch around a bit locating the release tab for the cable, and now that it's back together it now seems to work fine. Located a replacement switch just in case. May have to have someone do the replacement. Turn 80 in two months and tough getting under there.
Thanks for all you help and patience.
Frank

NoSlo · Aug 7, 2019

Motorcraft SW2258 Stop Light Switch (also Standard Motor Products SLS165)

(you don't need to do his modification)

Frank C Travanty · Aug 8, 2019

Thanks for the video and Part #s. I think Ford recommends the Motorcraft part so I will get one and put it in the glove box for when this acts up again. Wonder if the guy doing the video used a camera to see what he was doing? I found that kneeling on the ground out of the car gave a bit easier access to the switch than moving the seat down and back and laying on my back. Both tough.

NoSlo · Aug 8, 2019

All the wiring under the dash is tough, having done lots of electronics under there. Seat all the way back might help, if you don't want to go full on acrobatic, and lay upside down in the reclined seat.

Live view or pictures with a cel phone or pocket camera is certainly a new help in lots of things that were hard to inspect before. Some things, like the vehicle speed sensor, you have to do blind though.

rfried20 · May 17, 2026

Is this thread still followed? I have a problem with my shifter not coming out of park. I pulled the console out and found 2 broken thin gauge wires but I can’t see where the came from. But it shifted fine until I took the console out.

rfried20 · May 23, 2026

These are the wires I found

zoomlater · May 23, 2026

I think those are used for the overdrive button on the side of the shifter, my button stopped working awhile ago

Transmission Shift Interlock 93 SHO - Automatic Transmission

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