Tach not working

tfranko29 · 11-25-2003, 04:45 AM

'72 911T with '67 911 engine. I have a Perma-Tune and a Bosch Blue coil, but the tach has never worked, 11 years owned, I'm just starting to do my own maintainence and I want to get this tach working! Where can I begin looking? Thank you for the time.

Tim Walsh · Tim Walsh's Garage

Is there NO input into your tach or is it bouncing around and giving eroneous readings?

The first thing I'd do would make sure the purple/black wire is plugged in by your distributor.

Rot 911 · 11-25-2003, 05:04 AM

Is the tach wire in the engine compartment hooked up? Should be a purple/black wire.

tfranko29 · 11-25-2003, 03:14 PM

I will look for the purple/black wire connected to the distributor. There currently is NO input into the tach, it is not bouncing or giving erroneous readings

tfranko29 · 11-25-2003, 04:39 PM

The purple/black wire is connected to the dist. cap, then the wire runs, with a bundle of other wires, to the left side of the engine compartment and it plugs into a connector, then I wonder what

dhoward · dhoward's Garage

I think it may actually start it's run from the negative side of the coil....

shadow800 · 11-20-2009, 06:44 AM

hey Tim my name is GAry I have 83 sc my tach does just that jumps around with bogus reading and sometimes operates fine any ideas??

Thanks

MBruns · 11-20-2009, 07:19 AM

The SC tach is a magnetic triggered style, you may have to back date the tach or use an MSD box instead of the permatune.
Mike Bruns

silver_911 · silver_911's Garage

There is a different electrical connection to the tach for the different model years.
It is indeed a black/purple wire. On CDI cars up to 2.7 with 3 connections at the CDI unit, it is connected under the relay plate in the engine compartment. Hard to locate.
On cars with 6-connection CDI units, it is connected via the 14-pin connector at the back of the relay plate, thus needs to be reconnected.
Maybe after changing to the Permtune, the connection has been "forgotten"...
jens