3 pin CD Question
 

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.

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

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,

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.
http://forums.pelicanparts.com/uploa...1376947891.jpg
http://forums.pelicanparts.com/uploa...1376948158.jpg

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