Installing a start-stop switch
 

So, my ignition switch on the 78sc is not working anymore. It is the classic tumbler wear out, and I do not feel like spending $800 to replace it, plus all the aggravation to do the work.

I much prefer adding a start stop switch, which will be located to the right of the key, where a hole for the silly keypad was already there.

I have already added a wire to the terminal #50 of the ignition switch, and any 12V source provided to that wire will crank the engine, which is cool.

My problem is, I do not want the switch to crank the engine if the key is not on, for obvious security reasons. But everything I have tried so far will crank the engine, whether the key is on or off.

I tried unused slots at the fuse box in the trunk, but to my surprise they were all live whether the key was on or off.

I also tried the radio feed, which I am no longer using, but it turns out this one is also live regardless of the key position.

So my my question is, where can I find a 12V source that is turned off when the key is off, under the dashboard preferably.

Thanks in advance, I know some of you have done this before :D.

And if you have no idea what I am talking about, watch this video:

https://youtu.be/rReInvqc3J0?si=nNBWuNBNa4nx9tWF

There should be a wire to your old radio that turns off with the key and the other one you found that stays live all the time to keep memory functions.

I may be thinking about this incorrectly, but if it were a tumbler issue, wouldn't it keep you from being able to turn the key to the Acc, Run or Start positions? it sound to me like it is more likely the electrical ignition switch the the mechanical part of it.

If that's the case and you're willing to go after market our host has a replacement for $75. or genuine Porsche for $150.
https://www.pelicanparts.com/More_Info/UR96461301200.htm?pn=UR-964-613-012-00&bc=c&SVSVSI=0459

Correct, there is another switched wire to the radio. I used that one and it worked great!

There is a spring you can normally feel when you turn the key to the start position, so it automatically returns to the run position when you are done cranking. I do not feel that spring anymore, so I am pretty sure it is the tumbler that is messed up. One thing I may try is to have a new key cut, just in case it is the key that is worn, but I have little hope on that one…

The electrical switch also incorporates the starter position lockout, to prevent hitting the start position when the car has already been started. this forces you to turn the key to the off position before attempting a second start if the engine didn't start on the first attempt. it appears to me that this mechanism has likely failed and is stopping the ignition from being able to turn to the start position at all. if it were me, I'd remove the electrical switch from the back of the ignition switch and test it to see if it is the root of the problem. it is inconvenient to get to, but is only held on by 2 Philips screws. With the electrical switch removed you should be able to turn the switch on using a flat blade screw driver, to the run and start positions. if it will not let you turn to the start position even with it disconnected from the ignition mechanicals, then just replace the electoral switch.

I am moving forward with my switch install. I initially wanted to locate it to the right of the key where a hole already existed for a keypad, but the steering wheel lock is in the way, so that won’t work.

I could have drilled another hole in my dashboard, but I think I found a more elegant solution: I have this radio delete cover that was easy to drill, and I found a nice switch on Amazon that matches the Porsche logo I had on the cover.

Here is what it will look like:

http://forums.pelicanparts.com/uploa...1721687365.jpg
http://forums.pelicanparts.com/uploa...1721687365.jpg

Have you tested the original ignition electrical switch? Sure seems to me that that would be the easiest and simplest and cleanest solution.

I will check that too. But only because I found those switches for $29;).

Here is the final result, works great and looks great. Could I have replaced my ignition switch instead? Maybe…but I always wanted one of them startupwitches anyways;).

http://forums.pelicanparts.com/uploa...1721779430.jpg

I think it complements my LED gauges nicely:

http://forums.pelicanparts.com/uploa...1721779765.jpg