Diagnosing Tach Problem

[Quickstep192]

I recently switched from points to Pertronix. After the Pertronix install, my tach doesn't work. I went through a lot of wiring permutations before wiring the Pertronix properly, so I'm not 100% sure I didn't fry the tach in that process. What problem determination steps can I do to determine if the tach is fried, or if it's something else?

[Trackrash]

Some good info here. http://forums.pelicanparts.com/porsche-911-technical-forum/282209-tach-troubles.html#post8713065

[porschetub]

Thanks trackrash read the info,the OP didn't mention what CDI he was running so maybe thats the issue.
I would appear there is a need to have a tach that matches the cdi unit used atleast in stock form,think we are safe there,I wouldn't have thought the switching whether points or units like the Pertronix would matter......maybe the OP just has a non-related failure of his gauge.
The Pertronix instructions are a little lacking and in some cases the sellers of these don't state what is in the data supplied ,in my case I had to ditch a perfectly good set of solid core leads because my unit can't use them (Pertronix 2).
My impressions were that a tach-adapt was only required to read and modify non matching inputs,surely there must be people on here that have changed over from points with an otherwise stock system issue free ??????.

[Quickstep192]

I'm running the 3 Pin CDI

[Quickstep192]

I'm having a go at reviving this thread. I've read everything I can find, but haven't found info that is specific to wiring the tach in a '73.

As I mentioned in the original post, I went through a lot of trial and error wiring when installing the Pertronix. Is it possible I fried something or blew a fuse (is there any protection int the tach itself?)

Car runs great, just no tach!

Would love to get this squared away before winter weather (and road salt) come along.

Any guidance is greatly appreciated.

[Jonny H]

The early tachos are sensitive to the mark/space ratio of the signal. It should be approx 5% on, 95 % off. This ratio would have been set by the dwell time on the original contact points. Perhaps the change to Pertronix has upset this ratio? This would be governed by the width of the magnet/metal set into the plastic of the Pertronix 'collar'.

[wayne robson]

Hi Quickstep192,years ago i am trying to remember,think you take the wire connections from pertronix to the CDI box not the coil, or both, i will try and find another forum here
i read years ago. Wayne.

[Quickstep192]

This is the wiring diagram that I used to wire it up.





As I look at this, it seems that the tach should be getting the signal from the "C" lead from the CDI. If that's correct, I'm thinking it shouldn't matter what I have for points as long as the tach is getting the signal form the CDI. Do I have that right?

[wayne robson]

Quickstep192,--this may help. go to www.google. put in .
How to wire a tachometer on 1973 Porsche 911 with pertronix electronic.
good items there from dlague 2008.