OK, if you look up above it's clearly a '71 or '72 tach, the number is 230/41/10. I can't really read the number from your second photo but I am pretty sure it's a 72 date code.

You can confirm by telling me what the white plastic terminals say. If one of them is "C" then you have a later tach designed to be driven directly off the points. The earlier tachs have a pin labeled /1.

Here is the factory wiring diagram for the CDI ignition, very simple.

http://forums.pelicanparts.com/uploa...1134505008.jpg

John,
There is a C above the black/violet connection on the tach. I will double check the CDI connections.

Thanks,
Austin

:)
Great info. Subscribed.
:)

what about the early green faced tachs - the ones on the 1966, and '67(?) with the dual chrome rings?

I have a set of those instruments and like the way they look - I'd like to fit them into my '73 if it isn't too crazy an idea...

The mystery continues...
 

Everything at the CDI appears connected. However:
http://forums.pelicanparts.com/uploa...1234128902.jpg

1. There is a red/black wire connected to a red/white wire from a harness. The two brown wires are not connected at the rear deck inside.
http://forums.pelicanparts.com/uploa...1234128210.jpg

2. Two grey wires disconnected at the left rear and center fuse is not connected.
http://forums.pelicanparts.com/uploa...1234128375.jpg

3. One heavy green wire not connected at the right rear of the engine bay.
http://forums.pelicanparts.com/uploa...1234128485.jpg

Anyone have a 1974 wirring diagram?

Interesting thread. I have a basically stock 83 3.0 liter in my late production 71. I had a Permatune 6-pin, and the 71 tach seemed to work with it. Then, my Permatune failed. Now, I have a 6-pin Bosch CDI box in the car, and it runs great, but no tach.

So, it sounds as though I will need an SC tach.

Does anyone know whether running the Permatune with the old tach may have damaged the Permatune? Should I expect it to damage the Bosch unit, and disconnect the tach as a precaution, until I find an SC tach?

Thanks.

If anyone wants to use a CDI on a car with of these tachs, an MSD tach adapter box will alter the input from the CD box to work. This is of course in lieu of the silver Porsche part, which can be hard to find, IIRC.

Is it possible to adapt the 71 tach to work with the 6-pin CDI? This is certainly what I would like to do.

5. 1978-1983 Tachs. These are driven from the "TD" tachometer drive output from the six-pin CDI box because the points were eliminated in favor of a magnetic reluctor. According to the following thread, the SC tach signal is the same as the later Motronic:SC Thread

Hello I have an 3.79 SC Tacho. It came out of my 72 911F. I took it out because it had the black centercap.

No I would like to test it on my Function Generator.

It is a 231/1/5 12V/21000 IMP

3) +
2) TD
1) Ground.

I added 12V DC between + & Ground
and a 10V square pulse 50% duty cycle between TD & Ground.

I changed the frequency but it isd not working.

Am I doing something wrong with my test circuit?

BR
Bob

Bob, try a 38% duty cycle or less-- 50% would be appropriate for 4-zyl- and use 11V.

My old questions were unnecessary. My original 71 tach works fine off both the Bosch six pin and the MSD that I have in the car now.

Does anybody know?

Will an MSD 6AL ignition drive a tach from an 89 Carrera?

It works now, thank you. 304065
I have another tachometer which has a + , C, -. on a 914-6 project.

This unit runs with a 3 pin cdi. The C will be connected directly to the points on the distributor or to the C on the CDI?

The analog signal is a fast high signal (spike)when the points open the pulldown?

Br Bob

3. 1971-1973 Tachs. These appear the same externally but have been altered internally to be driven off the high-impedance circuit between the points and the Bosch CDI box. In the early 3-pin CDI boxes, there is a 33 ohm pullup resistor in the trigger circuit that would allow only around 425 mA to flow in the circuit. The tach must be sensitive to 11 volts and 425mA, which is why the later CDI won't drive the earlier tach off this circuit-- the earlier tach needs higher voltage.

4. 1974-1977 Tachs. I know these were driven off the CDI box, but I don't know when the CDI box changed from an "001" to an "008" or when the cutover from a 33 ohm pullup resistor to a 120 ohm occurred. With 120 ohms the input current is only 116mA so the tach must have changed somewhere along the line to match. If you send your tach to NH speedo to be recalibrated they want to know what CDI box you have, so this must affect the input value to the tach.

I posted this a few places with no response. It seems like I need a tach adapter, but which one?

I tried to swap in a '75 tach into the '79 turbo. The turbo has the stock cdi. The tach doesn't read. I tried another '75 tach, same thing. I checked both tachs on my '86 3.2 w/Electromotive hpv 1 and they both work fine. It's not a wiring issue, as I checked that multiple times with both tachs.

The '75 tach was set up work with ignition points. I suspect that the electromotive hpv may be compatible with a points type ignition and have a tach output that would drive the later as well as earlier tachs.

I'm thinking that your '79 will need a tach from the '78 and later mag coil (reluctor) type distributor.

But I could be wrong.

tach
 

did you see this???

http://forums.pelicanparts.com/porsche-911-technical-forum/627935-tachometer-adapter.html

Yes, I've been in contact with Bob. He's shipping me one of his units to try.

Subscribed:cool: