No reverse lights on 77 911

[rfaust6024]

I was told my car's reverse lights were not going on while backing up and was wondering how they work and where is the best place to start looking for a problem other then just checking the bulbs. I'm not really having much luck looking at the wiring diagram, but I'm not sure what I'm looking for. Any directions would be deeply appreciated. In regards to the wiring diagrams, is there anywhere I might be able to purchase a 11 X 17 complete colored wiring diagrams, where I can start and end a trace on the same page?
Thanks in advance,
Robert Faust
Redwood City, CA

[Rich76_911s]

There is a backup light switch on the bell housing of the transmission. Here is a photo of it:



Also there is a pin that activates this switch that can become worn down over time and becomes too short to activate the switch.

Here is a thread about the pin and testing the switch:

Back up light question


Hope that helps at least a little bit.

Rich

[James Brown]

That would be great however MOST wiring diagrams are not correct. The reverse light is easy to trace out. If the bulbs are good (checked with a good meter). jumper out the reverse switch on the transmission and see if they work. If they do then it could be the switch or the plunger in the transmission. If not keep going backwards till you find the open. Check the fuse, also. The factory manuals have the best diagrams.

[cary]

Some more input. Make sure the male pins are making good contact with the sender. Clean the sender sleeves with CRC contact cleaner. Then if needed spread open the male pins to make sure they're a good tight fit.
My .02c.

[rfaust6024]

Wow, this site and all you guys are incredible! I cannot believe there is such a fantastic site available where one with little or no experience can go and get technical information and instructions on how to fix problems. Again, thank you all!
Robert Faust

[boyt911sc]

Originally Posted by rfaust6024

I was told my car's reverse lights were not going on while backing up and was wondering how they work and where is the best place to start looking for a problem other then just checking the bulbs. I'm not really having much luck looking at the wiring diagram, but I'm not sure what I'm looking for. Any directions would be deeply appreciated. In regards to the wiring diagrams, is there anywhere I might be able to purchase a 11 X 17 complete colored wiring diagrams, where I can start and end a trace on the same page?
Thanks in advance,
Robert Faust
Redwood City, CA

Robert,

A very simple and convenient way to check the back-up lights and switch is by testing terminals #5 & #6 (14-pin connector). Terminals #5 & #6 are the two (2) terminals connected to F4 (back-up light SW).

Make sure that the back-up lights are good before proceeding to do this test. Follow these procedures:

1). Turn ignition switch to "ON" and press the brake pedal to test the stop lights. If the stop lights turn on, fuse #11 is good.
2). Split the 14-pin connector located in the engine bay fuse panel. Be very careful not to dislodge any pin from its original position.
2). Locate #5 & #6 (chassis side). With the ign. sw. turned "ON", #5 should have power (use a test light to confirm).
3). Use a suitable wire jumper to connect #5 terminal to #6 terminal. Back-up lights should turn "ON". If they do turn ON, back-up light SW is the problem.
4). If the back-up lights failed to turn on, either the back-up lights are not getting power or no ground connection.
5). Test the back-up light sockets.

BTW, the wire color for #5 is green/yellow and #6 is grey/brown. Keep us posted of your findings.

Tony

[mean_in_green]

Certainly check the bulbs and their holders first - the metal body part can oxidise and prevent the current from getting through. After that the switch and pin seem most likely candidates.

[Noah930]

Thanks for asking the question, RFaust. My reverse lights have also gone out and I haven't taken the time to figure out the problem, yet.

[Aurel]

Originally Posted by boyt911sc

Robert,

A very simple and convenient way to check the back-up lights and switch is by testing terminals #5 & #6 (14-pin connector). Terminals #5 & #6 are the two (2) terminals connected to F4 (back-up light SW).

Make sure that the back-up lights are good before proceeding to do this test. Follow these procedures:

1). Turn ignition switch to "ON" and press the brake pedal to test the stop lights. If the stop lights turn on, fuse #11 is good.
2). Split the 14-pin connector located in the engine bay fuse panel. Be very careful not to dislodge any pin from its original position.
2). Locate #5 & #6 (chassis side). With the ign. sw. turned "ON", #5 should have power (use a test light to confirm).
3). Use a suitable wire jumper to connect #5 terminal to #6 terminal. Back-up lights should turn "ON". If they do turn ON, back-up light SW is the problem.
4). If the back-up lights failed to turn on, either the back-up lights are not getting power or no ground connection.
5). Test the back-up light sockets.

BTW, the wire color for #5 is green/yellow and #6 is grey/brown. Keep us posted of your findings.

Tony

Hello Pelicans,

My 911SC failed inspection for backup light not working and I’d like to use the procedure above for troubleshooting. However, I am not very clear on what ‘split the 14 pin connector’ means, and where terminals #5 and 6 are located exactly. A picture would be great if anyone has tried the procedure already...
Thanks!

[Walter_Middie]

Aurel,

electrical issues after engine swap

This is for a completely unrelated issue, but it shows the 14 pin connector, where it is, and what it looks like when you split the connect in two parts to expose the pins.

[Aurel]

Originally Posted by Walter_Middie

Aurel,

electrical issues after engine swap

This is for a completely unrelated issue, but it shows the 14 pin connector, where it is, and what it looks like when you split the connect in two parts to expose the pins.

Great, thanks! Now I know what to deal with...

[pmax]

Before all that, I would check the reverse pin switch at the tranny first.

The wires connected to the pins can get frayed and loose, or worse like mine, given the mechanics where a wire pushes in a pin. Not the most robust of Porsche's design.

[Aurel]

It was very easy to unplug the 14 pin connector, and short pins #5&6 in the chassis side. This lit up the reverse lights, which tested the bulbs, sockets and wires.
Next I will unplug and short the reverse switch wires which will test the circuit all the way to the bulbs. If they works, then I will know for sure the reverse switch is the culprit, probably the pin.

[Aurel]

Update: I shorted the wires that come out of the reverse switch, but did not get the reverse lights turn on. Now I am confused. Does anyone know where the reverse switch wires end up? Directly in the wiring harness and to the 14 pin connector is my guess...

[timmy2]

Reverse switch wires run directly from switch to 14 pin female harness.
I have seen a lot of them cut by the starter due to lazy mechanics not unplugging during engine swaps.
Might check to see if there are crappy plastic splices along the length before it enters the harness with the starter wires.

[Flat6pac]

Amen on Timmy2^^^^
Bruce

[pmax]

Originally Posted by Aurel

It was very easy to unplug the 14 pin connector, and short pins #5&6 in the chassis side. This lit up the reverse lights, which tested the bulbs, sockets and wires.

I thought you were going to 'split the 14 pin connector' as per your previous post.

What is the thought behind Step #2 ?

Next I will unplug and short the reverse switch wires which will test the circuit all the way to the bulbs. If they works, then I will know for sure the reverse switch is the culprit, probably the pin.

[timmy2]

Pmax,
His first check with 14 pin connector Unplugged means all wires to the engine harness are disconnected.
He has tested the wiring in the through body harness to the lights and confirmed those circuits are working.

Next, he is confirming continuity from the wires back at the switch through the engine harness to the 14 pin connector, (plugged back in to male I hope) by shorting them together, the same as shorting the male pins at the male 14 pin connector that worked.
He has proven a fault in the engine harness.
Could be a cut wire, maybe just bad solder joints at he switch pins or at the terminal connector in the 14 pin female. (Maybe just dirty or loose female contacts)
He should test each wire to the female contact in the 14 pin connector next.

Isolate and test to determine where the fault is...

[Aurel]

Yep, Dennis pretty much described my thought process.
There was no need to split the 14 pin connector, not sure what the purpose of that was in the original method. I just ordered a new multimeter on Amazon to continue my troubleshooting...I will recheck the continuity of the circuit form the shorted switch wires all the way to the 14 pin connector, and if it is confirmed cut, may have to put new wires all the way form switch to 14 pins connector.

[timmy2]

I think some people express separating the male and female 14 pin connectors as splitting the connection?