I don’t understand wiring, no voltage to coil, no spark!

[SdeBrandt]

The car is a 1973.5 911T. I dropped the engine out for a refreshing, put everything back how I found it. Or at least I think so. Seems I’m not getting any voltage reading on the coil, of course no spark. The engine cranks over. Put in a new coil. Even bought another electric board, still nothing. Any suggestions? I’m about to pull the engine out again in case I missed something.

[brianlay]

no need to pull the engine for a simple electrical problem.
I think you forgot to plug in all connectors or something is not fully seated.

[timmy2]

You won’t see voltage at the coil on a CDI system.
Check your points are opening and closing properly.
Search “Dwell “.
Red wire plugged in Beside the CDI box?

[Dpmulvan]

Originally Posted by SdeBrandt

The car is a 1973.5 911T. I dropped the engine out for a refreshing, put everything back how I found it. Or at least I think so. Seems I’m not getting any voltage reading on the coil, of course no spark. The engine cranks over. Put in a new coil. Even bought another electric board, still nothing. Any suggestions? I’m about to pull the engine out again in case I missed something.

Throwing parts at electrical issues not a good idea unless you have money to burn.

[spoke]

Originally Posted by timmy2

You won’t see voltage at the coil on a CDI system.
Check your points are opening and closing properly.
Search “Dwell “.
Red wire plugged in Beside the CDI box?

If it has a CDI system, does the engine have the "green wire of death" from the distributor? That damn little wire cost me a $1000 tow across Pennsylvania for my '86 930. The replacement wire was $50.

[timmy2]

No “green wire” until 1978 6 pin or earlier 8 pin turbos.

[HarryD]

This post can be very helpful.

Originally Posted by Walter_Middie

If Marion's 1974 911 is stock, he won't have the infamous "green wire". He should have a 3 pin CDI:





You will not see any voltage at the coil like on a classic points and coil system, as the coil only gets a pulse from the CDI (shown in the AndrewCologne graphs above).

To get a spark to the spark plug in the engine:
First, you need power to the CDI.
Next you need to have a way to trigger the CDI

Then the CDI will send a pulse to the coil which will increase 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. Do you hear it whining? If so, you are getting power to it. 



2) Verify that the CDI is producing 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 of the spark plug. 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 your 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.