Tach goes wild when blinkers ....

[ertech]

Hi all
some times when I use the blinkers (right or left) the tach bounces in sink whit the blinkers . To see if it an alternator problem , when this happens I stop the the blinkers turn on all the headlights and fogs and this problem does not happen.My car is a 89 turbo

Thanks for your help

[dshepp806]

Grounds?

Doyle

[flat6pilot]

+1 for grounds.

Check out the grounding points on all four corners of the indicator lights. If the blinker can't ground properly it will find another path and may be interfering with the tach while trying to do this.

[86 911 Targa]

Originally Posted by ertech

Hi all
some times when I use the blinkers (right or left) the tach bounces in sink whit the blinkers . To see if it an alternator problem , when this happens I stop the the blinkers turn on all the headlights and fogs and this problem does not happen.My car is a 89 turbo

Thanks for your help

Your issue may be internal to the Tachometer.

Pull the Tach, and use this jpeg and your multimeter to verify
the proper grounds/voltages.

Your turn signal indicators operate on a common ground
which may be intermittent either at the Tach,
or at grounding point G116.

My bet is that the issue is internal to the Tach, the turn signal relay,
or an open ground, and your turn indicators have a new ground path
when you turn on the headlights.

Good luck,

Gerry

[304065]

Bad voltage regulator.

[kidrock]

I'm with 304065 on this, I think it may be a bad VR

[86 911 Targa]

Originally Posted by ertech

Hi all
some times when I use the blinkers (right or left) the tach bounces in sink whit the blinkers . To see if it an alternator problem , when this happens I stop the the blinkers turn on all the headlights and fogs and this problem does not happen.My car is a 89 turbo

Thanks for your help

If, as some have suggested, you have a bad VR,
place a voltmeter accross the battery, and start the car.

Your meter should read 13.5-14.5 Volts.

Turn on a few accessories, A/C, rear window defogger ect.

The voltage should not drop more than a volt.

A defective VR might read as high as 16-17 Volts.

If the VR is defective, DO NOT DRIVE THE CAR!

Good luck,

Gerry

[ertech]

the voltage ik ok . the tach did it again tonight for a few minutes with the blinkers than the tach did not respond for a few minutes than went back to life??
Thanks

[dshepp806]

How about those ground points?

Doyle

[dtxscott]

My money is on a ground issue with the tach. Why? The tach and turn signal indicators (green arrows) share the same ground and are pulling current from the same ground point.

One way to check is to turn on your flashers and see if the problem is "twice as bad" since both green arrows will be active instead of one.

HTH,
Scott

[uwanna]

Pull off the ground connectors on the ground stud located on the inside of the left front of the hood right by the battery. There's a bunch of brass connecters there. Clean each one with emory paper and reinstall. Bet your problem disappears!
I had the weirdest problem ever on my '80SC, some times when I honked the horn or used the blinkers, the wipers would take a swipe, HUH! Then when at night I turned on the headlights, the wipers would turn on and stay on! Checked everything I could think of, and in my checking of the wiring diagrams I noticed the wiper intermittant relay had a voltage path running thru the wiper switch to the washer motor. I pulled off the wires on the washer motor with the headlights on, and the problem disappeared! Got out my Hi Tech Techtronix meter and "read" ground connection to the washer motor. When I turned on the headlights I read 1-2v on the ground connection! The small voltage was running thru the washer motor windings and was apparently enough to go thru the wiring and "pick" the intemittant relay!
Cleaned all the afore mentioned ground connectors and Voila! problem fixed.
Ground loops can do incredible and amazing things!

[86 911 Targa]

Originally Posted by ertech

the voltage ik ok . the tach did it again tonight for a few minutes with the blinkers than the tach did not respond for a few minutes than went back to life??
Thanks

As per uwanna check the ground @ G116, per the CKT I sent you.

[RWebb]

uwanna-size the other ground star also - look up way high under the cowl (where it is hard to get to) on the driver's side in the corner

my 73 has one there

[ertech]

well it did it again put the flashers on and no problem only with nthe blinkers. acn it still be the ground G116?

[uwanna]

Did you completely clean all the ground connectors on G116 with emory paper and reinstall?