Points and condenser to CDI (1973.5)

[GJVGC]

Hello all,

I have a 1973.5 911T with CIS
The car has been running great with a Bosch blue coil ( 0 221 119 027) and condenser.
Issue with that set up is that i don’t have a working tachometer for some reason.

I noticed the 3 pin cdi plug in the car and looked into changing the setups to see if I could have a working tach.
I now have a CDI box ( 0227 200 001) and a Bosch Coil (black) ( 0 221 121 001) to install.

As mentioned the car ran great with the blue coil and condenser.
I installed the 3 pin cdi box and Bosch black coil and cut the green wire at the condenser as it would not be needed with the cdi set up but the car is not getting any spark.

Is there anything else I need to look into for this “conversion”

Thanks for any help!

[Trackrash]

The coil wiring is different when using the CDI. Here is the basic diagram. Note there may be a wire grounding directly from pin 1 to the fan shroud as well as a sheilded ground to the CDI box as shown in the second pic.

[GJVGC]

Thanks Gordon!

Looks like my CdI box is correct at least


Now what plugs into the wire off of the points? The condenser used to wire up to that black wire off the points



Thanks!

[HarryD]

Originally Posted by GJVGC

Thanks Gordon!

Looks like my CdI box is correct at least


Now what plugs into the wire off of the points? The condenser used to wire up to that black wire off the points



Thanks!

The Black wire from the CDI goes to the points.

[GJVGC]

Harry,

To confirm, this one?


Also, my black/purple tach wire seems to be connected to that black wire from the cdi.
Is that good for the tach to get the signal?

[GJVGC]

That’s my tach wire and the black wire from the cdi. Those go to the points?

[HarryD]

Originally Posted by GJVGC

Harry,

To confirm, this one?


Also, my black/purple tach wire seems to be connected to that black wire from the cdi.
Is that good for the tach to get the signal?

That looks correct. Check with an ohmmeter.

The tach (purple/black wire) gets it's signal from the points not the coil in a CDI System. See the attached wiring diagram.

[HarryD]

Originally Posted by GJVGC

That’s my tach wire and the black wire from the cdi. Those go to the points?

Yep.

[HarryD]

Originally Posted by GJVGC

Thanks Harry,

So it would be ok to connect the purple/black wire (tach) and the black wire from the cdi to the points?

Yes, exactly as shown on the factory diagram.

[GJVGC]

Any particular place this ground need to be? Or anywhere on the engine case ok?

[HarryD]

Looking at the wiring diagram it goes on the distributor.

[HarryD]

Looking at the blow up of the wiring diagram on Post 9, you will see two wires that are black/white squares. One is connected to Terminal 1 of the Coil and the other is connected to the body of the distributor. Both of them go to the grounding terminal on the CDI (see the full drawing in Post 7 above).

I am assuming you can read these diagrams. Is this correct?

[GJVGC]

Thanks Harry,

I was just making sure of the connections so I would not fry any of the parts.
I installed everything as shown but not getting any spark.
Checked and I am getting 12v to the red wire off the cdi box connector.

[spyerx]

FWIW, PartsKlassic makes some really nice harnesses that make this plug and play, and also one that will allow use of Pertronix w/o any additional wiring. I'm glad not to deal w/ points any longer...

https://www.************.com/p-1544-3-pin-cdi-wiring-harness-with-pertronix.aspx

[HarryD]

Lots of threads on this topic. Here’s one:
How do i check a coil with a timing light??

To get a spark to the spark plug in the engine. Several things need to happen. First, you need power to the CDI. Next you need to have a way to trigger the CDI (the points do this by opening and closing). Then the CDI will then send a pulse to the coil which will increause the voltage and send it through the high tension lead to the rotor and to the selected spark plug. You need to verify that each step in this chain is working.

1) Verify that the CDI is getting power.

2) Verify that the CDI is producing power to make a spark. You can do this with a "telegraph" test. Take the high tension lead off of the center of the distributor and put a spark plug on it. Ground the threaded part. With your plug attached to the center lead, open the distributor, remove the rotor, place your key in the run position, and manually open and close the points. Each time you cycle, you should see a spark from the plug. If you do not, you may have a bad CDI.

3) Verify that the coil gets a signal when you crank. Replace the rotor and distributor cap. Leave the plug on the center high tension lead. Crank the engine. Do you see a spark? If so, you are getting spark to the distributor. If not, your point gap may be off or there is some other problem with the connections.

4) Verify that the spark goes to the spark plug wires. Reattach the center lead to the distributor. Attach you spark plug to one of the leads going to the cylinder spark plugs and ground. Crank engine. If you see a spark you may have a timing problem. If no spark, you have a problem with your rotor or distributor cap or your wires are improperly seated.

Do a search here as there are many threads on this topic. Look especially for the ones by early_s_man. Warren (RIP) left a great deal of knowledge on troubleshooting this problem.

[GJVGC]

UPDATE!

Thanks for all the help guys!
I got the car running with the CDI and Coil using the wiring diagrams on this thread.
The ground I was questioning worked great to the distributor body.

One issue is that my tachometer is still not working. The black/purple wire is connected to the points.
Does the tach wire go through the 14 pin connector on the rear electric panel? Where can I trace the wire to?

[GJVGC]

You can see the black/purple tach wire to the points on the distributor

[timmy2]

As per the drawing Harry posted:
Black/purple from the points goes to pin 9 of the 14 pin rear connector, then it goes through the rear relay panel harness to pin 8 of the more forward 14 pin connector, then directly to the back of your tachometer.

[GJVGC]

Thanks Dennis,

I confirmed the black/purple wire at pin 9 rear connector.

Where is the more forward 14 pin connector located? Further up on the rear electronics panel?

[timmy2]

Yes, less than a foot closer to the driver than the back one. Below the CDI box.