Distributor & Points question

[356robo]

On my 70 911, how do I wire the distributor? Does the only wire from the distributor attach to the positive side of the coil? If not, where?

Thanks in advance,

Rob

[304065]

Rob,

Before I dispense the advice, can you tell me how it is that your 70T has no wiring?

OK, here is what I would do. First some background.

When any wire work on a 911 is undertaken it is important, absolutely critical, to use the correct size and color wire to match the factory. The size, well that's easy enough- that's a function of the power-handling capability of the particular wire gauge, and also making it appear original. You don't want to use a huge fat wire when a small one was used.

The other thing is the colors-- a lot of guys use speaker wire, zip cord, lamp cord, whatever, and then when the time comes to diagnose problems with the car, they are left trying to figure out which identical brown wires go to where. Bad idea, at least if you ever want anybody to help you. When people ask for electrical advice here on the forum and the car has been botched by some prior owner, half the time it's impossible to help them without actually standing by the car, which is, after all, the whole point of this forum.

So rant over. . . but with a recommendation to contact one of www.ynzyesterdaysparts.com, www.riwiring.com or www.eagleday.com and get the CORRECT wires for what I'm about to tell you.

A further complication is that it depends on when your 70T was made. If the production date was very late, it may have different wiring insofar as the factory changed the tachometer drive circuit in October, 1970. However, the October, 1970 cutoff date is in the 1971 model year, so you're probably using the old system.

Do you have a metal can in the engine electrical console that says, "einbau senkrecht klemmen unten" on it? This is an "intermediate unit" that drives the tach. When Porsche switched over to CDI ignition in 1969, the tachs (until October 1970) were driven by this intermediate unit, which is basically a coil that dumps a couple hundred volts into the tacho drive circuit.

Anyway, here are some comments on the wiring diagram. The basic idea is that the distributor has a single wire that goes from the points to the CDI trigger terminal. The CDI has a +12V power input. Then the CDI has a +460V power output directly to the ignition coil. Finally, and very important is the CDI ground, this is a metal tab on the case. A way to remember is "B" for Battery, "C" for contact (the points) and "A" for ACHTUNG, don't electrocute yourself! The other coil primary terminal goes to ground of course.



Well, that is the diagram that I have handy, I see it doesn't include the intermediate unit. Here is one from Sherwood Lee's page that does.
http://members.rennlist.com/911pcars/SL33-lft.pdf

You can see clearly that the intermediate unit, identified as #10 in the diagram, has an input "B" which is from the coil 15 terminal (the ACHTUNG terminal!), an input "A" which is a ground wire (the giveaway is that it is brown) and an output "C" which is black with a purple stripe- THIS is the wire that drives the tachometer.

Clear as mud? I welcome any questions. Be very, very careful working with capacitive discharge systems, the capacitor remains charged after the power is disconnected from the unit and could cause personal injury or property damage. Good luck!

[356robo]

John,

Thanks for all the info. To answer your questions:

1. The previous owner had installed a cast iron early distributor dated 4/66 with Pertronix. I have purchased and wish to install a date correct distributor using points. I am trying to verifiy the correctness of the current wiring to the Pertronix.

2. My car has a build date of 10/24/69.

3. Yes, I have the metal can that says "einfau senkrecht klemmen uten" on it.

I intend to match the wiring as close to original as possible. The existing Pertronix wires are attached to parts of the wiring harness. The red lead goes to a cable bundle near the console that you spoke of. The black lead attaches to a bundle near the distributor.

I'll print and read all the links you provided and contact you by email or PM if I have any further questions

Thanks again for your help.

Rob

[304065]

The Pertronix has only two wires, a +12v and a ground. It works on Kettering-ignition by interrupting the ground, same as the points. When the ignition is turned on, +12V is present at coil 15 and the coil 1 is at ground. The coil engergies and the magnetic field builds up. When the hall-effect circuit in the Pertronix is triggered, the Pertronix interrupts the flow of current between 15 and 1 together, causing the field to break down and the ignition current to flow between coil 4 (high-voltage) and ground.

So the Pertronix should be connected to the coil positive and the coil negative (and grounded to the points plate inside the distributor). Everything else should be as factory.

Good eyes, spotting the distributor date code! I'm always looking for good cast iron distributors BTW. I have an obsession with them.

[304065]

he Pertronix appears to have been wired according to Pertronix instructions. The red wire goes to a 2 into 1 splitter attached to a bundle of wires at the electronics console. The black wire from the pertronix to a 2 in 1 splitter that includes the black/purple lead of the tach.

Here's what I believe. I need to remove the red pertonix lead and leave the existing 2 into 1 connector as is. I need to connect the insulated spade on the side of the new distriubtor to the 2 into 1 connector that includes the black/purple lead.

Before we go any further, what are you using for an ignition box? Bosch CDI? MSD? Nothing? That's a key question.

[356robo]

I'm currently using factory CDI unit.

Rob

[304065]

[356robo]

Thank you John and the others who contributed. I was able to complete the transition back to points. Car idles and runs great.

Rob