Tachometer Ground

[DMC Fanatic]

My tachometer has been a little erratic and bouncy from time to time. Can someone tell me where the ground wire is located? I was going to try and clean that first and see if thats the problem. Thanks!

[DMCMW Dave]

My tachometer has been a little erratic and bouncy from time to time. Can someone tell me where the ground wire is located? I was going to try and clean that first and see if thats the problem. Thanks!

It grounds in the cluster with all the other meter grounds on the left side. More likely a bad connection in the white-grey coming from the ignition ECU, or at the connector right on the back of the cluster.

[DMC Fanatic]

Is the ignition ecu mounted behind the driver's seat behind the rear deck?

[DMCMW Dave]

Is the ignition ecu mounted behind the driver's seat behind the rear deck?

Yes, but if the problem was there you'd feel the engine stumble too. The same output drives the ignition. The ECU is the one under the steel deck.

[Bitsyncmaster]

The fuel pump shares that instrument ground. If you have a weak ground it could cause some tach problems. Do you have a stock (blue) ignition coil? Do you use the stock ignition resistors?

There have been some owners with bad tachs so that could also cause your problem.

[DavidProehl]

Also check your fuses. I had a crusty fuse in my car that was resulting in a bad ground. My tach would jump around when the A/C kicked on. Replacing the fuse fixed the problem.

[DMCMW Dave]

Also check your fuses. I had a crusty fuse in my car that was resulting in a bad ground. My tach would jump around when the A/C kicked on. Replacing the fuse fixed the problem.

Good catch. I've had one or two where if you wiggle fuse #5 you can make the voltmeter read anything you want. The tach is powered by the same fuse.

[DMC Fanatic]

I replaced my fuses last year along with a new oem ignition coil. Do the blue ignition coils tend to cause problems? The tachometer issue is very minor and if I cant figure it out I'll have Rob Grady look at it when I take the car there next month for service. Thanks for the help so far.

[Bitsyncmaster]

I replaced my fuses last year along with a new oem ignition coil. Do the blue ignition coils tend to cause problems? The tachometer issue is very minor and if I cant figure it out I'll have Rob Grady look at it when I take the car there next month for service. Thanks for the help so far.

The blue coil is the stock one. So your coil is good. The coil loading and coil resistors do affect the signal the tach gets but so far I have not heard anyone with tach problems even using another coil. It seems our tach has a pretty go design for that input signal.