MSD wiring help needed for 911T 1969

[BartdeBruijn]

Recently I had some ignition cut outs that were very difficult to trace down back to the root cause. It happend all on different occasions and circumstances.

The big culprit I expect was/is the CDI box. I drive a 1969 911T with Bosch CDI and a ballast resistor (I thought to protect / make the the tachometer work). I have a standard Marelli distributor with points.

To buy myself some peace of mind I bought a MSD 6A ignition control, MSD blaster coil and a tach adapter.

After reading a lot of threads I still have a question on the wiring.
Do I have to connect the balast resistor together with the tach adapter. If so, how and if not will my tachometer survive.

I tried to make a schematic wiring drawing. All is clear except the part in the dashed box.

I hope someone can shine his light on this as I like to drive the car the last good days in the Dutch autumn ;-)

Cheers,
Bart

[1969911T]

My 69T(German) did not come with a CDI.

I have the same set up(same MSD, Marelli, Blastercoil and tach adapter.)

The tach wire that was originally on the negative side of the coil is connected to the tach wire from the MSD. So a very “weak” voltage gets to the tach.

You do not need the ballast resistor.
If you need more, Let me know and I will take pics and find my wiring diagram.
This runs great and allows you to make up an emergency coil and wire setup where you can run with a new coil without the mSD!
Steve

[BartdeBruijn]

Hi Steve,

thanks for reply!
Mine is also a German car however after half a year imported to the USA and now in the Netherlands.

Will try your setup and report back!
(Will be the weekend ;-)

Cheers,
Bart

[1969911T]

Found my schematic

[BartdeBruijn]

While solving an intermittent ignition problem running an old CDI I ordered and installed an new MSD setup.

After installing I had no spark and while using the fault finding in the manual and using the white wire —> grounding I had a spark (many strong ones as promised by MSD)

So it works but when using Bosch distributor there was no spark.

While digging down I found that the rotor has an infinite resistance between the two green arrows. This seems strange/wrong to me and while testing a new Marelli rotor this measured (close to) zero ohm.

People encountered this also or wrong thinking from my side?
I will order a new one….
Thanks,
Bart

[1969911T]

There should be continuity between the places marked with green arrows. Usually 5,000 ohms resistance. If the rotor is an rpm limited rotor maybe it “stuck” open when it rev limited.
Rotors for CDI should have very little resistance.

The newly made Marelli rotors have no resistance, so are fine for CDI. The kit for rebuilding a Marelli comes with a 5k resistor built into a connector that fits between the coil and the center plug wire of the distributor for a standard ignition
Steve