Converting later green wire for early turbos

[boosted79]

As most know the presently available green wire 930-602-907-01 which is correct for the 78 and later 930's won't function correctly on the early turbos which used a blue wire 930-602-911-00 which is NLA. All because the dizzy rotation was changed from CW to CCW in 78. Here's an easy way to convert it to use on an early turbo. I know some have just reversed polarity at the CDI connector or changed the polarity right where it comes out of the dizzy. For the shield to work correctly it has to be connected to the ground, this accomplishes that.

Remove the female faston connectors from the white cover that plugs into the dizzy by depressing the faston barbs with two small jewelers screwdrivers. This is what you have, shield is on right as it goes into the dizzy.


Then flip the block 180 so shield is now on the left


Twist each wire 180 so the barbs are on the bottom


Lift the barbs back up so they will grab correctly and insert the connectors back into the white plastic cover with the locating tab on top.


You will notice that the slots in the block for the retaining clip do not go all the way thru the block. Open them up all the way with a hack saw so the retainer will slide up into the now upside down block. Also you will have to trim some plastic off the now bottom of the block so the retainer will slide up enough so the retainer screw hole lines up with the hole in the dizzy. Reinstall the separate black plastic piece that slides over the white connector cover and you are done. Here's the final result.


If you are splicing the new green wire into your existing harness make sure the shield that is now on the left side of the dizzy connector goes to ground.

[356911930]

Great job Boosted79! Another file to save for future use, thanks.

Rahl

[boosted79]

So the reason I did that was because my understanding was that the polarity must be reversed to use the green wire on the early CW distributors. Now I see this and he says the rotation has nothing to do with the waveform?? So now I'm confused. Does that mean that the polarity does not have to be changed on the green wire or what for it to work on a '76??

I have a CCW distributor and a CW distributor. They both have the impulse coil with the "A" on the left and the "B" on the right looking into the distributor. On the CCW dizzy the "A" is the center wire and goes to pin "7" on the CDI box. "B" is the shield and goes to 31D.

So my understanding from reading all of the "green wire" threads on here and the tech forum was that the green wire polarity has to be reversed for the CW dizzy which means shield on left "A" and center wire to "B" on right.

But he's saying it doesn't matter?

I don't know how the 76 was wired because it had a couple wires twisted together with some hacked connectors onto the impulse coil and they just fell off when I removed the dist.

https://youtu.be/kQTDGpZ614w

[T77911S]

the shield does not matter because the signal Is an AC signal kind of like what is in your house. that is it goes positive and negative. so the shield is not really a ground


here is my 86 with the wires BACKWARDS. (to trigger my MSD)



the CD triggers off the steep slope, but positive to negative for the 86. just flip the signal over in your head. it WILL trigger off the long slope but the timing will be waaaay off.

[flightlead404]

Originally Posted by T77911S

the shield does not matter because the signal Is an AC signal kind of like what is in your house. that is it goes positive and negative. so the shield is not really a ground


here is my 86 with the wires BACKWARDS. (to trigger my MSD)



the CD triggers off the steep slope, but positive to negative for the 86. just flip the signal over in your head. it WILL trigger off the long slope but the timing will be waaaay off.

^^^ The important thing is that on the triggering part of the slope (could be on rise or fall depending on the device you are triggering) the "zero crossing" is steep. When it isn't steep the elecontrics has a hard time figuring out exactly when the zero crossing is, and at higher rpms that small time diff can make a big timing diff.

[Bigtoe32067]

I'm so confused and now my brain hurts

[boosted79]

"I'm so confused and now my brain hurts"

You and me both.

OK, so let's simplify this and leave out polarity, waveform, electrons, zero crossing and all that electrical jargon.

In a pre '78 CW rotating distributor should the center wire go to the "A" pin or the "B" pin? The "A" is on the left and "B" is on the right looking into the dizzy.

Then at the CDI box the center wire should go to pin "7" and the shield goes to 31D. Yes or no?

[356911930]

^^^

Thank you!

Rahl

[T77911S]

you were talking about polarity,
I just thought I would show you what you were talking about.

you will either have to do trial and error or connect an Oscope to a pre 78 and check the signal out of the dist.
if the dist rotation was changed at the same time the CD's were it is a very save assumption that the triggering polarity changed as well.
if the polarity is different then it will be correct for the MSD.

I have looked at the diagram for both CD's, they don't indicate any kind of "polarity".

wont the plug that plugs into the CD have to be changed also. if so, just make the polarity swap at the CD plug end,

[Tromas]

Hi Guys

Very interesting topic! I just spent most of August trying to debug a very poorly running 77 930. I'll share my experience later in the reply.

Some in this thread have expressed confusion on the video from Kurt. The point Kurt is making in the video (posted by boosted79) is that regardless of rotation direction of the distributor (CW or CCW) the pulse waveform is the same going to the CDI box. He also demonstrates that the waveform takes opposite shape if you change the polarity (positive becomes negative, and negative becomes positive) relative to the CDI box.

Now the fact that a newer green wire (930-602-907-01) has polarity as indicated by the second picture below (and as indicated in Kurts video), means positive is flowing on the shield of the green wire, and the core becomes the shield. At the same time if you look at the first picture of the wiring harness of my 77 930, you can see once connected together there will be a, let's call it "cross over" between shield and positive in the timer jr junction, but that doesn't necessary mean you have a polarity swap.





This other video by Kurt talks about the impact on timing if polarity is swapped (around 6.00):
https://www.youtube.com/watch?v=v9HEiqqXG_o

If you do have a polarity swap on your early 930 turbo the car runs poorly, and you won't be in doubt, it will cut out in ignition at idle, and behave erratic at higher RPM. If you have have a newer green wire on your distributor and polarity swap (poor running car), Kurt suggest what you swap the terminals in the timer jr female connector in the wiring harness to solve the problem. I disagree (...respectfully of course) with that approach, I'm concerned that changing the pins in the timer jr female connector in the wiring harness will effectively make the positive signal run in the shield all the way up to the CDI box, and the signal will is exposed to electrical interference which the shield is intended to protect against (defeats the purpose off the shield).

So back to where the thread started, I do not think the suggestion about flipping the terminals at the female connector of the green wire at the distributor will solve the issue, on the contrary I believe this will cause a polarity flip, and the car will run poorly because the timing will be off on the car as shown in the (other) video from Kurt (around 6.00).

I think for early turbos what you need to do is:

1) Ensure that you have proper polarity and that positive runs in the core, and the shield is the ground. Your car will run and you won't be in doubt if polarity is not right (trust me the car will run poorly :-) )
2) With a newer green wire you can have the polarity correct, but you will have the signal run on the shield up until the time jr connector junction, and I believe this makes the signal connection exposed to interference, so flip the terminals on the green wire on both ends - meaning both at the female part at the distributor, and at the male time jr connector, that way you preserve polarity and the shield runs all the way from the distributor to the CDI box

I'll be experimenting with 2) next week when I get a custom made green wire.


So as indicated above I changed the wiring harness on my 77 930. Before I took the old wiring harness out it was a well running car, but after I put the new wiring harness in the car would barely start and run. After checking the timing gun I could see the timing was waaaaaaaaaaay off (retarded), to the point where I had to reindex my distributor to get the timing back closer to 5-7 deg ATDC @ idle. It was a real head scratcher why I had to reindex the distributor as the car was a running car before I took the old wiring harness out. I got the car running after reindexing, but it was running erratic at higher RPMs, and I could barely adjust idle timing by rotation the distributor without the engine stalling. It wasn't until I started digging into the polarity that I realized that the polarity was reversed, and after correcting the polarity I had to re-reindex the distributor back to where it came from. The car runs normal again.

Personal Learning: POLARITY MATTERS :-)
Next (project) Learning: Will a custom made green wire make a difference

Thanks
Thomas

[Jonny H]

The direction of rotation has no impact on the waveform polarity. No need to swap wires when using Bosch parts. All 911 Turbo and SC ignitions are negative edge triggered.

The only reason to swap polarity is when running MSD which is positive edge triggered.

[T77911S]

the signal in not a plus and minus signal like a DC voltage. its an AC signal

think of a guitar cable or microphone cable. its not DC. the signal goes both positive AND negative just like the AC in your house. you can flip a 2 prong plug that goes into an outlet and it does not matter,. its just a coaxial cable.

as far as the early CDs and later ones, I am assuming (as does the OP) that the early boxes trigger on the POS edge and the later ones trigger on the NEG edge.

look at the pic I posted. the horizontal line in the center with the bigger hash marks represents ground or 0v. so anything below that is negative voltage.

I am assuming the early CDs are 8 pin boxes. if so just get a 6 pin connector and flip the wires AT the CD unit and don't worry about it.
or just put in and MSD and you should not have to flip the wires.

[Jonny H]

^. As I said, all Bosch 6 and 8 pin units units are negative edge triggered. Early 8 pin units same trigger signal as later 6 pin, irrespective of distributor direction.

Trust me on this, we have rebuilt hundreds of these unit and make our own too!

[Jonny H]

info and bar trivia only:

If you really want to fry your noodle, as stated Early 8 pin boxes use the same trigger as a 6 pin but the tacho drive signal is high voltage. This means that early Turbo tachos are high voltage like 69/70 cars and earlier. All 6 pin Turbos have low voltage tachos like the SC.

In other words, for 2 years only, the early Turbo tacho has the high drive input like an early car. Crazy huh?

This means that an early Turbo cannot use a later 6 pin box or the Tacho won’t work. Conversely, if you use an 8 pin box on a later car the tacho will work for a bit and then get fried by the high voltage.

This is a problem for anyone building a 934/935 replica using 8 pin boxes unless they have a genuine 934/935 tacho (also high voltage). If you spend a ton of money converting a post ‘70 tacho to look like a 934/935 item it will ultimately be destroyed.

This is not common knowledge so I’m putting it out there.

FYI. We offer an 8 pin replica box which can be configured either as low or high voltage tacho drive.

[boosted79]

"The direction of rotation has no impact on the waveform polarity. No need to swap wires when using Bosch parts. All 911 Turbo and SC ignitions are negative edge triggered."

I agree. But does the generated voltage signal now flow through the shield on the new green wire on a CW dizzy? I found a cheap scope on Amazon that I am going to buy so I can check it all myself.

[flightlead404]

Originally Posted by boosted79

"The direction of rotation has no impact on the waveform polarity. No need to swap wires when using Bosch parts. All 911 Turbo and SC ignitions are negative edge triggered."

I agree. But does the generated voltage signal now flow through the shield on the new green wire on a CW dizzy? I found a cheap scope on Amazon that I am going to buy so I can check it all myself.

The rigol 1040z is a great buy and easily hackable to enable all the features. s/b around 400 I think.

[boosted79]

My idea of cheap is a Quimat at $43. I'll probably never use it again, not into EE stuff unless I'm forced to be.

[Jonny H]

Originally Posted by boosted79

"The direction of rotation has no impact on the waveform polarity. No need to swap wires when using Bosch parts. All 911 Turbo and SC ignitions are negative edge triggered."

I agree. But does the generated voltage signal now flow through the shield on the new green wire on a CW dizzy? I found a cheap scope on Amazon that I am going to buy so I can check it all myself.

Only in so much as it returns to ground through the shield. Shield is connected to ground at the CDI unit. They all do that though, irrespective of CW and CCW.

[boosted79]

Well I got my little Quimat scope up and running and set up my own Sun distributor machine.

The bottom line is the center wire has to be connected to terminal "A" on the impulse coil and the shield on "B", regardless of rotation.

Here's my Sun dizzy machine LOL



Here's the trace with the center wire to "A" and the scope positive probe to pin 7 at the CDI connector, scope neg. probe to the shield at the CDI connector.



That's what you want.

Connect the center wire to "B" and the shield on "A" and this what you get.



That won't work.

Connections at the CDI block.



The Quimat is a neat little piece of kit for $43, maybe I'll even use it again sometime but it was worth it just to be able to see all of this myself.

[flightlead404]

Heck that is a pretty neat thing. I might buy one for when I don't need to lug out the Rigol!