Reverse (Backup) Lights???

F

Fife

Registered
Hello,

I noticed this morning that my wife's 1994 Mark VIII did not have any backup lights on when she was coming out of the garage. I had her slowly move the gear selector and the lights do come on half way between park and reverse.

I am wondering where the problem lies. I did recently put on a new MLPS (neutral safety switch) to correct the problem of the car intermittently revving up like its in neutral when cruising on the highway. The MLPS corrected that. The part came from Autozone (Duralast) and I do believe I installed it correctly...I don't think it can be installed incorrectly with the detent fit.

What can be done about this? Do you think it has anything to do with the MLPS or is there something else I need to adjust/repair?

Thanks,
Fife
 
If they worked before the MLPS fix, then I would say start there. You say they come on between park and reverse. So the bulbs are getting voltage and good. Sounds like it is an indexing issue with the gear select/MPLS.

When driving on the highway, my car feels like it's shifting into Neutral, then it goes back into gear. What gives?

The MLPS (Manual Lever Position Sensor) may need replacement. This is what 'tells' the transmission what gear you have selected. When it fails, it may intermittently report the shifter is in Neutral, causing the symptoms above.
Click to expand...
 
The MLPS has alignment marks that must be lined up on the installation. If I remember correctly, it is aligned with the shifter in neutral.
 
Why would the shifter have to be in neutral? The MLPS and the shaft on the transmission that it fits onto have a slot or detent. Alignment is guaranteed since you cannot install it unless the slot lines up perfectly.

I am not sure if the reverse lights worked before or not...I think they did but not sure.

Is there another way to correct the problem or do I have a faulty MLPS? I really don't think installation alignment is the issue issue. I do believe I was in park when I installed the MLPS. I just rotated the switch until the slot lined up and it slipped on easily.
 
The holes where the bolts go through the MLPS to mount to the trans, are slotted. This is what you use to align the switch as explained previously.
 
Fife said:
Why would the shifter have to be in neutral? The MLPS and the shaft on the transmission that it fits onto have a slot or detent. Alignment is guaranteed since you cannot install it unless the slot lines up perfectly.
Click to expand...

The factory tech would use a special tool.

Manual Lever Position Sensor
SPECIAL SERVICE TOOL(S) REQUIRED

1. Remove nut securing manual control lever to manual lever position sensor.

2. Turn manual control lever to NEUTRAL position.

3. Loosen two MLP sensor retaining bolts.

4. Align MLP slots using Manual Lever Position Sensor Alignment Tool T93P-70010-A.

5. Tighten retaining bolts to 9-12 N-m (7-9 lb-ft).

6. Install nut retaining manual control lever to MLP and tighten to 16-22 N-m (12-16 lb-ft).
Click to expand...

There are two alignment marks on the sensor that must be perfectly aligned with the shifter in neutral. With the shifter in neutral, loosening the two mounting bolts will allow you to rotate the outer housing to achieve proper alignment.
 
I don't think one can see those alignment marks when the sensor is on the car and I don't have an alignment tool.

Would the following work?

Loosen two bolts on sensor.
Put car in reverse.
Rotate sensor until reverse lights come on.
Tighten bolts.

Wouldn't that get one very close to proper alignment?
 
Fife said:
I don't think one can see those alignment marks when the sensor is on the car ...
Click to expand...

Sure you can...

Image000.jpg
 
What year is your Mark VIII? My car is a 94 and I am pretty certain that my sensor is different. Mine is about four inches long and two inches wide and it looked exactly like the original. They are functionally alike but physically very different.

That is a really good picture as well. I could barely get to my sensor with the exhaust pipe right in the way.

What about my idea of aligning reverse with the reverse lights (if I cannot see the alignment marks)? I may be able to with a mirror...not sure.


Thanks,
Fife
 
That pic is from the '93. I have a '96 as well and I'm confident the MLPS is the same.

Looking online, the '93-'96 MLPS replacement part numbers are the same:

F3LY- 7A247- A
F5AZ- 7A247- A
F5AZ- 7A247- AA
F5LP- 7F293- AA

The physical difference you mention has me wondering if the switch really is the same.

As far as the method of alignment you mention, I suppose it would be worth a try but I suspect with a small telescopic mirror and flashlight you could easily eyeball the alignment marks.

Do you have any issues with the shift cable?
 
I fixed it in about five minutes today. It was easier to access than I had remembered. When I originally installed the MLPS, I was at my Dad's and he didn't have the ideal tool for the job. Anyhow I just put it in reverse and rotated the MLPS until the back up lights came on. Then I took it for a test drive and everything is working fine. Hey thanks for the input...I appreciate it!

Fife
 
I'm glad you fixed it but I'm curious, while you were there, why didn't you just use the alignment marks?
 
Glad to hear it's working. :)

Did you check the alignment marks in neutral? If not, be alert for symptoms of shifting to neutral when driving. That is a symptom of a malfunction with the MLPS.
 
I looked for the alignment marks...did see the line that stated "Neutral" next to it. I sort of lined it up with a notch but wasn't sure exactly what I was supposed to be lining up with. So I just used the back up lights as my "alignment tool." Should I have any problems with the shifting into neutral problem, I will go back and do the textbook alignment. The reason I changed the MLPS out in the first place was for the shifting into neutral problem. Everything doing fine as of today. Thanks.
 
When in neutral, the line you saw should extend towards the inner rotating part and line up with another line as if it scribed across the two pieces.

You can see it in this pic...

Image000.jpg
 
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