Ignition sw failed?

[boomboom]

Anyone ever taken the electrical side of the ignition sw apart to look at the contacts/swiper for failure on a mid-year car? Engine will not shut off when key is turned home position. Everything else shuts off except engine and tach. Thanks for any suggestions/input.

[boyt911sc]

Originally Posted by boomboom

Anyone ever taken the electrical side of the ignition sw apart to look at the contacts/swiper for failure on a mid-year car? Engine will not shut off when key is turned home position. Everything else shuts off except engine and tach. Thanks for any suggestions/input.

What year/model is the car?

Tony

[boomboom]

1977 911 Targa with 3.2 DME. Thanks for any suggestions or ideas if that part of the switch can be taken apart.

[boyt911sc]

Originally Posted by boomboom

1977 911 Targa with 3.2 DME. Thanks for any suggestions or ideas if that part of the switch can be taken apart.

boomboom,

The ignition switch assembly consists of two parts, the mechanical (locking unit) and the electrical (tumbler). See attached pictures below:





The electrical section has 2 sections. One piece (tumbler) attached to the ignition switch (mechanical) and the other has all the electrical wires connected. You could pull or unplug the piece that has all the wires and expose the two (2) tiny screws that secures the first portion (electrical) to the ignition switch.

Removing these 2 hard to reach fasteners is a challenge to most DIY'ers. Do a search about this project. You need to remove the driver's seat and work on your back to access to get the 2 screws off. I rate this task as very tedious and frustrating. Good luck.

Tony

[boomboom]

Thanks a bunch Tony. I am pretty sure the problem is in the mechanical part of the switch. I'll describe the problem:
1) Key is put to the engine off position and engine continues to run.
2) Unplug battery and engine continues to run.
3) Remove fuse 11 to fuel pump and engine shuts down

Any other thoughts?

[boyt911sc]

Originally Posted by boomboom

Thanks a bunch Tony. I am pretty sure the problem is in the mechanical part of the switch. I'll describe the problem:
1) Key is put to the engine off position and engine continues to run.
2) Unplug battery and engine continues to run.
3) Remove fuse 11 to fuel pump and engine shuts down

Any other thoughts?

boomboom,

#1: It could be true. But you could confirm your assumption by separating and testing the electrical sections (tumbler) and the ignition switch. Instead of using the ignition switch to start/run the engine, use a screw driver to start the engine by turning the electrical part. But you have to separate the tumbler from the ignition switch which is the hard part of the task.

#2: That's not surprising. The alternator is supplying the needed power. Unless the alternator charging cable is separated/detached from cable cluster to the battery.

#3: Fuse #11 does not supply power to the FP. It is fuse #16.

Tony

[boomboom]

Tony,
I am using the wiring diagrams from Prospero Garage and it shows fuse 11. I have wired according to this diagram and I'm now wondering if I may unintentionally have caused this problem. Do you know where I can find a reliable wiring diagram for a 1977 911 with air cond and pwr windows? This is really becoming a nightmare! Can't be that difficult! Thanks in advance.

[ossiblue]

boomboom,

Is this condition of continued running with ignition "off", new or did you just get the car and this is what you discovered? I ask because of your comment that, "I have wired according to this diagram..."

I agree with Tony that the problem is likely in the electrical module of the switch rather than the mechanical. Yes, it's a PITA to remove the electrical part but you can easily check to see if that is, in fact, the problem without any sweat.

If you have a friendly Porsche shop near by, you can ask to borrow an electrical part for the switch (you can do this at their shop or maybe they will do it for you--it takes less than two minutes.) Simply unplug the wiring harness from the back of the ignition switch and let it hang under the dash. Plug in the borrowed electrical part, use a flat blade screw driver and turn the switch to the "on" and "start" postions. Then, turn it off and see if the engine shuts down.

If everything works okay with the borrowed component, buy it and now you'll have to go through the contortions of actual replacement.

If the borrowed switch doesn't solve your problem, it's possible (as you speculated) that the mechanical part is at fault. The mechanical part has a "+" shaped pin that goes into the electrical component and turns the switch, much like you can do with a screw driver blade. Sometimes this pin twists or even breaks off because it's just pot metal. I am doubting that because when this happens, there isn't enough strength in the pin to crank the switch over to "start", which yours consistently does but you can never assume anything when diagnosing a problem.

[boomboom]

L.J.
That's an excellent idea/suggestion. I'll see if J3 Racing locally has a spare switch that I can borrow and perform the test. I'll also see if I can shine a light with a mirror to see the potential pin concern. Have you ever taken the switch apart and tried to fix the contacts/swiper internally? I only say this if J3 does not have another switch to borrow. Thanks.

[boomboom]

All,
One more thing, are fuses 17 thru 20 suppose to share a common buss? Thanks.

[boyt911sc]

Originally Posted by boomboom

All,
One more thing, are fuses 17 thru 20 suppose to share a common buss? Thanks.

Yes. Fuses #17-#18-#19-#20 are bridged. BTW, I am using a factory shop manual wiring diagrams as reference for your '77 car.

Tony

[boomboom]

Thanks Tony. Seems like I'm going to have to eventually spring for a shop manual. Do you show color codes for wires to all the fuses? In specific I would like to know for fuse 11 and 16.

[boyt911sc]

Originally Posted by boomboom

L.J.
That's an excellent idea/suggestion. I'll see if J3 Racing locally has a spare switch that I can borrow and perform the test. I'll also see if I can shine a light with a mirror to see the potential pin concern. Have you ever taken the switch apart and tried to fix the contacts/swiper internally? I only say this if J3 does not have another switch to borrow. Thanks.

boomboom,

You could not see or inspect the ignition switch drive pin even if you use a probescope!!!! The only way you could visually inspect the said pin is to remove the electrical part of the ignition switch. Taking off these tiny screws is a nightmare. And when you install them back, my suggestion is to replace them with allen type screws.

If you could get them out under 60 mins. from the moment you start the work, I'll give an A1+ rating for ingenuity and versatility. Keep us posted.

Tony

[djbrand1]

I found it way easier to remove the entire assembly, then replacing the switch while off the car. Getting to those little screws holding the switch on while still under the dash just seemed like a nightmare. I had the entire tumbler/switch out in less than 15 minutes, replaced switch in 5, another 5 for cleaning out the tumbler, and maybe 15 to reinstall.

[Skip1]

+1. I agree taking the entire assembly out is easier unless you have great dexterity. I had the same problem last year and it was the internal workings of the electrical part of the switch. It is a non-repairable parts (pressed together - and not very well I might add). The screw driver solution works very well to try to rotate the electrical switch. It looks like a plus sign '+' once the mechanical part is removed.

[boomboom]

Wow, after all the challenges and learned lessons I think I will try to just remove the bad boy and replace the switch component. Don't think I am up for another back breaking experience. I've had enough with insulation removal on the floors and then the fuse panel redo. Marking all the wires and adding length to old short wires has taken a toll on this old back. Thanks for all the insight and suggestions.

BTW, J3 here in Atlanta did not have a spare switch to help with troubleshooting.