3 pin CD Question

[Rslevin]

I have a '73 911 and getting no spark. CD is humming and wiring seems to be correct. I am getting no voltage on terminal A, 15 on the coil from A terminal from the CD box. Shouldn't this be at 12V? Thanks for any help.

[Flat6pac]

The wiring is getting old. The core wire with the white cover , surrounded in steel ground cover. is breaking down and if you meter the wires you might find the white wire is common to ground.
Bruce

[Rslevin]

I thought that was a ground. I have 2 grounds running from the D terminal on the CD box. One goes to the distributor body, the other the coil ground. I am not seeing a white wire, nor any reference to that in the wiring diagram. Can you be more specific as to where this wire is and what to do about it? Thanks,

[E Sully]

You will not get a voltage reading on the A terminal. The B terminal should have the 12+V reading. If it is whining, then the 12V is there.
If you have the original CDI wire harness, the A and C wires are white with gray exterior over the shielded wires. B is Red.
The 2 shielded wires combine the shield at the CDI with a common connector to the ground tab. Heat shrink is used to cover the shield.
Here is how I test the CDI. I connect a spark plug lead to the coil, Instead of using the points, I touch the C wire to the ground tab on the CDI to get a spark. Second picture is a CDI harness timmy2 is making up for a replacement harness, using white exterior instead of Gray.
A CDI can whine and still not work.

[Rslevin]

Thanks for that info. To be clear, of the two braided shield wires, one goes to the coil minus, the other the the distributor body? I did Ohm out the shielded wires from the ground to both the Coil A and the points and neither was grounded. I'll check the CD as you described. Thanks again, Rich