please help with tach

[targa6911s]

Hallo,
I have a trouble that I´ve seen on many threads of this forum ( My tach doesn´t work and I´m still working on it.
I´m planning to visit the West Coast in July, so I´m in a hurry trying to determine the cause of the failure. (Connection or Tach itself)
If failure is due to the tach I´m thinking on give it to NH, that I also have read that is the preferred place to go.
First of all I was looking at the back of my gauge and have detected that the numbers don´t match with the ones described on this thread:
Tachometer Compatibility Chart
As You can see in the next picture, nmbrs are close, but not alike the 1969 (my car).


So the first question is if I have to assume that the tach is period correct with 1969 S ?
In that case, if I also have to assume, that the wiring diagram of the 69 S applies to mine?
For the next step the following picture gives a better view of the wiring.


I was thinking about checking the continuity of the cables (back of the gauge vs. engine bay).
Would You please give me a hint on telling me which ones to peer?
The next 2 photos show the elements to match in the engine bay.



Thanks in advance for your time-
Ed

[targa6911s]

bump

[304065]

Ed, I can't see the face of your tach in the photos so I don't know if it's a 911S or not, but it's definitely a 2,0 liter tach from a 911 (you can tell by the "6 Zyl" for six cylinder on the back and the screw-on brackets to hold the gauge in the dash-- later ones are held in only by the gasket.)

OK, do you have power to the tach on the blue/yellow wire? Measure with a meter between the connection and the brown ground, should be +12v.

You can barely see in the photos but the terminals are labeled +12, 6 (not used, that's for six volt cars), /1 (black/violet wire, this is the tach input from the intermediate unit) and - for ground. Make sure all the wires are on tight and ensure there's no corrosion on the brass terminals. Be careful handling them, the wires are old and brittle-- take a little piece of FINE sand paper and clean the corrosion off the contacts. From the photos things look OK.

In the engine compartment things get tricky because 1969 was unique in terms of the electrical system layout. The big black relay that says "nicht werfen" or "do not drop" is a "slow-acting relay" which was used for the cold-start mechanism on the '69-only enrichment solenoid on the pump. The 70- cars don't have that because they used a cold-start system in the aircleaner.

Download the wiring diagram for the car here and spend a day studying it.


1969 911T,E,S electrical wiring diagram

Now, it looks like something is missing- there should be a metal can that says "einbau senkrecht klemmen unten) which means "install with contacts facing down"-- this is the "intermediate unit" required to drive the tach off the coil. It's a long story but basically Porsche didn't change the tachs until october of 1970 to drive off the CDI points trigger directly-- so there's an intermediate unit connected to the coil that drives the tach off the coil primary- when the primary current breaks down this unit sends a pulse forward through the black/purple wire. Your intermediate unit seems to be missing, it looks like this:



If you can't find one of those, you can have NH speedo convert the tach to work with the CDI directly, just like the later tachs.

Basically the violet wire connects to terminal "C" of the intermediate unit and goes to the tach. "A" is the ground, and "B" is the high-voltage input (460V) from the output terminal of the CDI Box (which is labeled "A" on the CDI box, don't get me started on why these things aren't the same).



The box you posted is the defroster relay.

The other box mounted perpendicular to the electrical console is the speed switch or "RPM transducer."

That is a non-standard voltage regulator in green.

Did your tach EVER work? Probably not given that there is a missing part.

Good luck!

[briancoates]

Hi Ed

I have a wiring diagram for the 69 model that shows very clearly what colour wires go where.
It is a large .jpg file that you can zoom in on and trace all wires. If I post it here the size will be reduced and be of no use. PM me with an email address and I will send you the files.

Cheers Brian

[targa6911s]

Hi,

Thanks Brian. I have already got the diagrams for 68,69,70 and over. My actual problems are:
1- As the car was dismanteled for a full restoration, and I didn´t see the tach working ever, I also have doubts about the correct re-wiring.
2- My ability on following the wiring on the car. That is why I am looking for some practical guidance over the actual wiring.
Anyway, many thanks for your quick support.

John,
This is a picture of the face of the tach. As it apparently has the original mark over the 7k I assume it matches for an “S”.


My doubt (no more after your answer) was if it was a 69 or not.

The next picture is one of the whole stuff on this side of the engine bay. They are labeled so as to refer and identify the elements easily (With this I am asking you John, this new favour).


As you can see these are the only elements present in this place.

The answer to your final question is NO. I have never seen it working.

For both of you (Brian and John) thanks again, your quick answer reinforces my idea about the kindness of the people in this forum

Ed

[briancoates]

No problems Ed, I have attached a view of the tacho from my diagram, as you can see it is rather useful as the diag shows actual positions on the gauge the wires should be connected to. The 3 terminals you need to be worried about are the 3 across the bottom in the plastic block. The others are only lights. looking at the back of the Tach they should be from left to right: blue with white bands across the wire, Blue with yellow stripe running along the wire and black with purple stripe running along the wire.
It is hard to tell from your pics but it appears the colours are in the wrong order.

Remember rewiring is done at your own risk!

With the whole diagram you can see exactly what they connect to and to what positions, helps with continuity testing.

Good luck, wish I only had wiring problems...lol

[targa6911s]

Hi John,
You are very right. Cables (from the color point of view) were wrongly connected.
I switched the blue-yellow and the black purple ones to the position your diagram and Porsche's one indicates.
In this step I have a new problem.
I just have one blue-white cable, and it`s connected to the top of the gauge, where R & L blinking lights are (as diagram indicates). I didn’t see another blue-white cable
And a new question:
I have followed the wiring diagram in all the blue-white cable (that in my car is apparently missing) and as You can see, after passing the fuse box and changing to white, it goes to the “terminal connectors” and then ends in the “HEAD LAMPS” ?????!!!!
OK. First of all I know have to re-read my electricity notes from the Univ. but meanwhile, can you please tell me if this connection is relevant for the RPM. May it be a ground cable through fuse #2 of the Fuse box II ?
Gratefully
Ed

[targa6911s]

Hi Brian,
In my rush for answers I didn’t see your signature, I thought was John’s answer.
I apologize and thanks you for the drawing and details.
By the way, I have another question for you.
Waiting for the answer to my last post I was searching the blue-white cable and looking at details of the wiring diagram when a primitively-basic doubt came to my mind.
When looking at the gauges on the wiring diagram, you could see that they are presented as they were seen from the driver’s position, not from the hood’s point of view.
The same happens with the Left and Right representation of the connectors of the blinking lights of the same gauge.
Does that mean that I have to assume the same criteria for all the other connections?
In the case of this particular interest: Are the cables blue-white and black-purple showed to us on the diagram as if they were seen from the driver’s position?
In plain, the blue-white cable has to be connected to the clip on the driver’s side and the black-purple cable to the one on the other side?
Thanks.
Ed

[briancoates]

No problem.

Good point, in the diagram the speedo is on the right of the tacho that may help. Send me an email to briancoates@live.com.au and I will reply with the full diagram it should help.

[targa6911s]

OK, here I am again but this time just for closing the thread,
Tach is working fine
The "intermediate unit" was very well hidden behind the fuel filter.
It also had a connector unplugged. Precisely the C position, with the signal to the tach on Pos.1.
I found the missing (and also hidden) cable and from then on, everything is OK now.
Thanks again John, Brian and the people behind this forum
Ed

[briancoates]

No problem Ed, hope we were of some help. Glad you got it fixed with no cost.... always a bonus.