Cleaning up engine electrical, where to hook up Condensor wire

[Kevins911]

I'm cleaning up the electrical in the engine bay of my '69. All I have back there is a coil and the voltage regulator. No more CDI box, just a switched 12v going to the coil. The only thing I have a problem with is where to hook up the condenser wire now that there is no CDI box. Any help is appreciated. Thanks in advance.

Kevin

[eapcpa]

You need to give more Info and pics. I am not sure a CDI coil will work properly with a standard ignition. Why would you eliminate the CDI?

[Kevins911]

Doing some research, looks like my condenser wire hooks up to the - side of the coil, along with the tach wire. Terminal 15 gets my switched 12V. The coil is just a transformer, shouldn't matter if it's CDI or not. Why get rid of it? It's 40 years old. Keep it simple like the 914 and VW's, the only thing that can go wrong is a broken wire

Thanks
Kevin

[Kevins911]

here are some pics so far...

[HarryD]

Originally Posted by Kevins911

Doing some research, looks like my condenser wire hooks up to the - side of the coil, along with the tach wire. Terminal 15 gets my switched 12V. The coil is just a transformer, shouldn't matter if it's CDI or not. Why get rid of it? It's 40 years old. Keep it simple like the 914 and VW's, the only thing that can go wrong is a broken wire

Thanks
Kevin

Kevin,

There is a reason Porsche moved from a Kettering Ignition a long time ago. For Hi-performance engines, you may not get enough spark energy to light off your engine charge. This will be most evident at the higher rpms that the small displacement engines like to run at.

Also, since the CDI has a much hotter signal to the tranformer (coil), the step up ratio does not be as high to get a good spark. The CDI produces something like 400 volts to the coil. Your kettering system provides only 12. This means that your spark voltage is reduced from 40,000 volts (the coil is 100 to 1) to 1,200 volts.

Do you still think you will have enough spark?

[Kevins911]

When I first got my '71S the electrical was a mess. I measured the voltage to the coil and it was less then 1 volt, if I remember corectly it was .3 of a volt. The car still ran, and pulled right to redline. Of course there was a huge difference when I installed the MSD unit . I'll measure the voltage going to my spark plugs when I'm done, just to compare. I will eventually install an MSD unit in this car too, right now I just want to get it running, and 1200 volts should be just fine. Do you really think that a 40 year old CDI box with old leaking capacitors is still going to produce 400 volts to the load side?

Thanks
Kevin

[HarryD]

Originally Posted by Kevins911

When I first got my '71S the electrical was a mess. I measured the voltage to the coil and it was less then 1 volt, if I remember corectly it was .3 of a volt. The car still ran, and pulled right to redline. Of course there was a huge difference when I installed the MSD unit . I'll measure the voltage going to my spark plugs when I'm done, just to compare. I will eventually install an MSD unit in this car too, right now I just want to get it running, and 1200 volts should be just fine. Do you really think that a 40 year old CDI box with old leaking capacitors is still going to produce 400 volts to the load side?

Thanks
Kevin

If you are measuring the volts on a CDI system, you will need a scope as the pulses are too quick for a multimeter to register.

For a bit of learning:

From this web page (http://www.autoupkeep.com/LCChapter11.htm):

Step Up Voltage
One of the purposes of the ignition system is to step up voltage. Basic electrical principles were presented in Chapter 7, Electrical System. You know now that automotive batteries have a surface voltage of about 12 volts DC. This is sufficient for running accessories such as lights and radios, but not powerful enough to ignite the air-fuel mixture within the combustion chamber. Common voltages at the spark plug can range from about 10,000 to 50,000 volts. These high voltages are created with a coil, a step up transformer.

and this Web Page outlines the problem with a Kettering System in our cars: http://books.google.com/books?id=OIbOxjVp-q8C&pg=PA21&lpg=PA21&dq=voltage+to+ignite+engine&source=web&ots=2MFzOnesEk&sig=Y4h1XkrxHndJQY9MmtXEHCcQ5_k.

[Kevins911]

great, thanks for the info Harry. I'll be putting an MSD in this thing pretty quick then. This will at least get me up and going.

Thanks
Kevin

[911pcars]

For simplicity, a regular points/induction system will get you going until you upgrade to the suggested ignition (Crane, MSD, etc. with pointless trigger).

The condenser lead connects to the ground side of the coil/points circuit, in parallel with the stationary contact and the neg. terminal of the coil.

http://holdenpaedia.oldholden.com/images/e/ef/UnBallastedCoil.gif

There should be a ballest resistor in the source voltage connection to the coil so during normal running, source voltage is only about 9 volts to prevent overheating the contact points. During engine starts, the ballest resistance is bypassed so the system can produce max. secondary voltage.

Sherwood

[304065]

Kevin,

For starters, here is everything I know about early car electrical systems, including how to hook up a Bosch CDI. Information about the Ballast resistor and relay included there as well.

Before there was BHKZ: SWB engine electrics

You don't need a pointless trigger, a good set of points lasts thousands of miles when it's triggering a CDI box or an MSD. Some like them, though, but the trouble I have is you can't tell when they break, whereas with points it's all out in the open.

You should eliminate that solid state facet fuel pump while you are in there, and use one up on the crossmember next to the steering box if possible. A 69T probably had a Hardi, these are actually available new these days.

I would suggest that you make the wiring look as original as possible. Use electrical tape where the factory did, don't use any of that GM-style split loom stuff as it just fills up with water and tends to raise the eyebrows of anyone experienced with Porsche electrical systems. I've looked at cars to buy and seen that stuff and had visions of hundreds, literally hundreds of hours of diagnosis to figure out what the PO hacked so I could make things work correctly-- electrical diagnosis is hard enough when what's in the car conforms to the factory wiring diagram.

My recommendation would be to install a Bosch CDI following the diagram in the thread above, this is a very reliable, proven solution that the factory itself adopted for the 911E and 911S in 1969.

[Kevins911]

Thanks for the info John, I finished up all the wiring and the car wouldn't start, so I used your diagram and quickly wired in a spare Bosch CDI box I had. She fired up right away!! I see the light now The spark off the switched 12v was just not enough. I will permanently wire in the CDI box tomorrow, it's still a nice clean look in there. I used electrical tape (super 88) to wrap the harness that I built, no GM split loom stuff, all though I'm not really concerned about making the harness look stock. Still very simple back there, any problem can easily be found. I'll post a pic when I'm done.

Thanks
Kevin