My current tach is from memory a 72 911 one,looks nice but that's about it,the needle is unstable as rpm changes and not reading right.
I have a later tach which is from a 76 and has 8 pins on the back (only 3 used) can anyone tell me what pins 2,5 and 6 are for ?.
1 x purple black to engine loom,
1 x brown earth,
1 x red/black switched power.
I need to know which wire to which pin,thanks in advance

All it needs are those three connections - 12v switched, ground, and tach signal. Your problem is that it doesn't have an adapter for an early car.

Try looking for a "tach adapt" which converts the tach signal to something your tach can understand.

But which pins do I connect to? otherwise your answer is well ....useless sorry ,already have tachadaptor in there and know I have to change the jumper connection for the early to late input rate.

I just did this on my car; I have a 2.7 with a 911 2.7 tach and electromotive ignition. I don't recall the exact pin out, but they were clearly marked on the back of the tach (engraved). I did not need to use all the pins, just like you. My tach works just fine, but having said that I had it rebuilt at No Ho speedo, and they asked me what kind of ignition I was using.

You can figure out ground and +12 volts.

My question to you is where your tach signal is coming from?

And, have you ruled out the tach itself as being free of problems?

Lastly, go find a 2.7 wiring diagram. It will tell you what each pin means.

Check this out, it's on pelican - GOOGLE IT.

All the answers you seek are there. Most of the tach connections are illumination.

The factory 911/914-6 ignition circuit is a capacitance discharge ignition. The points are just a low voltage trigger. The tach connection is hooked to the points and that doesn't provide the required voltage to drive a stock tach. Porsche didn't redesign the tach innards when they went to the CD ignition, they just slapped a tin can "Tach amplifier" on the cars. So your tach wont' work correctly.

Unfortunately these are unavailable from Porsche any more. The concurs 911 guys pay big money for them when they can find them.

Fortunately, you can use an aftermarket aftermarket tach adapter such as this:

MSD Tach Adapter

The MSD box is a CD ignition that generates multiple sparks. So their tach amplifier works on a 911/914-6.

I have one in my car right now. I put it in when the "tach amplifier" died. Works perfectly. Too bad I don't need it any more. The new motor is Motronic.

Thank you gentleman for your replys.
I did search for a very long time and found diagrams but they don't match the wires to the numbered pins on the tach as mentioned they are only a represention of one.
My ignition is Pertronix ignitor II and Permatune blue CDI box it works very well.
I contacted Bob @ Ashlocktech and he confirmed my initial set-up of the tachadapt ,I have no history on the tach I'am running however.
I'am merely wanting to test the spare I have against my current one and as the spare is a match for the CDI i'am fairly sure I won't need the tachadapter.
Click to view attachment
The top pin on the tach is marked as #2 and the 2 lower ones are #5 and #6.
Hope this is more helpful information,thanks.

That doesn't look like the tach I have (74-77) nor does it match the pin out I gave you on the diagram, which was for an SC. Are you SURE that is a 2.7 tach?

It's not rocket science. There is a part number on the front of the tach, google it or look it up on the PET to find out for sure what year it is. Buy a 911 Haynes Manuel. It has diagrams for every year 911 up to 89. I used a 3.2 / 930 tach with both my 2.7 with webers and my current motronic 3.2. All I used was the Haynes Manuel and pet to figure it out.
Here's my notes.
91164130106 = Euro / 05 = USA = 84-89
2=blk/Purple= signal
5=Positive
6=Negative

Get the part number off of the front, so we can look it up.

Checked the number and you are right,not my info it was from the guy I bought it off but feel foolish/ripped off cause that was what I was told by the seller .
It's a 3.2 one 84-89MY ,not sure if it will work,I remember reading these are electronic and get there signal of the ECU.....not 100% sure.
So it goes to prove I don't know sh#t about 911 tachometers,and the seller didn't give a rats when I dealt with him,also purchased 911 oil tank off him just for the filter console he tells me "you could sell the tank on its worth good $$'' it arrives with a huge dent in it ,his reply is "you could blow it out with compressed air it will be fine"....enough said ended up with on me again.
Ok back the the original question any of the 3.2 powered guys out there have an answer

I might have a tach for a 2.7 that I can trade you for the 3.2 tach. Let me check tomorrow.

Thanks a lot Steve that's what I needed,I will try to get them swapped over today and see what happens,will be great if this one works then I can get my engine timed @ full advance and get my carbs balanced.

mepstein would be happy to trade but this tach is a bit rough looking,up to you really.

Have been in contact with Bob @ tachadapt and he has been super helpful,clever man ,he thinks my sourse for tach signal is wrong,so he sent me some schemetics to go thought what I have ,appears its better to receive a tach signal from the cdi rather than the coil,all food for thought.
Contuary to what pertronix says its not plug and play with all 3 pin Porsche supplied CDI's,he mentioned there coil isn't a match for the permatune I have,Perry pointed this out in one of his emails and he was right...sorry Perry.
So Bob summed up by saying my system will work fine but I'am not getting full bang for buck so I have 2 options replace the coil with the correct one or remove the Permatune from the system.
I have yet to decide.........