Where is the Tach wire on the engine?
 

I have an 84 911 and the tach suddenly stopped registering at all. I am wondering if a wire is loose. Where is the tach sensor on the engine?

Rick, it runs off the DME.

Yup. What he said.

Hrm. Well bummer. I was hoping there would be a wire that might be loose.

Ok, so my tach was working fine one week and then poof! Nothing. All the other indicators on the dial work fine, even the idiot light. Any ideas where I should start? Should I pull the tach and check the back of it? I find it a little hard to think the connection would have come loose from back there...

Bump...any help on where to start trouble shooting this tach?

You might try an external tach (RPM meter) and tap into the back of your tach to see if you are getting any signal at all.

Nathan,

I'm not sure if this will help or not, but here goes:

The wires that come out of the DME that go to the tach come from slot #11 and #21. The wire out of slot #11 is a black wire, and the one that comes out of the #21 is a black/violet wire. Did any of those come loose on the back of the tach?

Isn't the tach sensor associated with the two sensors that are right off of the starter ring gear, near the clutch. I know the engine speed sensor is back there, but I am not sure if that is what send the signal to the tach or not. I think if that wasn't functioning you'd have bigger problems than a non-functioning tach though.

Do you have a Bentley Manual. I pulled mine out to try and help, but I haven't ever messed with this stuff yet. And I am just pulling at strings trying to get something together for you.

If you need something else out of the bentley manual that might help let me know and I'll try my best to find it for you.

Rich

The DME requires rotation speed of the engine; not the wheels.
Wheel speed is used for the odometer; not the engine rpm.

There's a sensor picking up the wheel rotation speed of one of the axles, close to where they connect to the transmission. The wire runs through the tunnel (under the hatch between the rear seats) forward.