Tachometer not working!!!

I recently got a 1986 targa carrerra, the alternatoer was bad, PO told me about it, it is being rebuilt tommarow.

The tack also is not working, I do have a haynes manual on order, but would like to get some idea's before it getts here.

The tach is just dead.... The PO said it would work everynow and then when he hit a bumb.

I was wondering where should I check, I have looked for loose wires, and checked fuses.
I am kind of stuck until I get a wiring diagram.

I will also check on the bently manual.

Thanks for any help

I sounds like a wiring problem. Don't just check for lose wires, remove each connector from the back of the tach and clean the conector and contacts. It could also be an internal issue with the tach.

Another place to check near the CDI unit in the engine compartment. If you look at the wire harness that plugs into the bottom of the unit, a single wire comes out about 8-10" . The wire has a push connector, pull it apart and make sure the connector is making contact (that was the issue with mine)

Just a few ideas.

I'll agree with cleaning connectors is a good (cheap ) start. Don't know how many used cars I've bought that I solved many problems tracing to dirty corroded connectors --- the Porsches I've bought (especially ones seldom driven or that have sat for a long time) have not been exceptions and due to their higher cost have always been my best $ bargains when it turned out to only need a clean connection, not a new part!

It sounds to me like you have some bad grounding around your instruments! Didn't you say that your alternator warning lamp bulb was good when you tested it with an Ohmmeter?

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Warren Hall
1973 911S Targa

Warren,
Yes the alternator bulb tested good with a Ohmmeter.

I will check the ground later today on the gauges, I am also picking up a Manual this evening too, it's just the haynes but better then nothing, I will check on the bentley too.

I also hope to get the alternator back today too.

Thanks for your help.
Bruce

I would retest your tach once you get the rebuilt alternator. I had a dead tach (among other things) that was fixed by swapping out the regulator (which on the SC is built into the alternator). Just a thought...

Lee

Well I got the new alternator, and the Tach is still ot working.
I checked all the grounds that I could find, cleand them.

It l;ooks like the Tack goes Directly to the DME, so I guess the Tach could be bad.

Any other suggestions
thanks
Bruce

Bruce,

If you have access to an oscilloscope, or know someone who has one, it sure would be useful to know if you have some pulse activity on that line to the tach from the DME control box. It may not be the tach. itself, it might even be the connector at the DME unit under the seat!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 10-27-2000).]

Warren,
I can borrow an o-scope from my neighbor.
I treid to reseat the DME connector, but could not Get the connector all the way off, without unbolting the DME unit.
I take it off this weekend, I also have some good contact cleaner.

The shift light also does not work, but that is directly related to the tach.

Thanks
Bruce

I was able to follow the signal from the DME all the way to the connector on the back of the Tach. so the tach is dead.
I opened up the tach and there is a burnt resistor inside, so It looks like I need a new on.

Can the tach be easily fixed buy a shop??

Thanks
Bruce