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> What is happing to my tach?, TAch drops out at about 4500 rpm Also drops if I use directional swithch. Then bounces all over
moneysmarts
post May 11 2026, 09:48 AM
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What's going on here? I've had the same set up for 20 years (2.0 D-Jet with MSD 66AL)
Now at 4500 rpm the tack drops out, then bounces wildly. Also if I use the directional signals, the tack drops. Ill try to add a little video
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moneysmarts
post May 11 2026, 09:49 AM
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Hmmm
Video wont upsoad
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IronHillRestorations
post May 11 2026, 10:01 AM
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Try changing the points
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moneysmarts
post May 11 2026, 10:08 AM
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QUOTE(IronHillRestorations @ May 11 2026, 08:01 AM) *

Try changing the points


Thank you.
I will try that.
Since I've owned the car (25 years +) I have never gapped the points. I thinks Slits told me they were useless with the MSD, and to just leave them alone.
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moneysmarts
post May 13 2026, 02:41 PM
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Well. I have a nice clean dizzy with new points and condenser, but my tach still drops to zero and bounces back up and down at high revs. Smooth and steady from 1000 to 4500, then, boom. falls right off as the car is still reving higher.
I also noticed that at any RPM, if i use my directionals, the tack also freaks out.
Almost like some electrical gremlin. I think all my grounds are good. Maybe I have bad bulbs that are causing feedback?? open to any recomendations
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Spoke
post May 13 2026, 03:41 PM
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QUOTE(moneysmarts @ May 13 2026, 04:41 PM) *

I also noticed that at any RPM, if i use my directionals, the tack also freaks out.


These 2 electrical systems should be isolated from each other. Sounds like you've lost the ground on the tach or some other wiring issue.
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porschetub
post May 13 2026, 03:58 PM
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QUOTE(moneysmarts @ May 14 2026, 08:41 AM) *

Well. I have a nice clean dizzy with new points and condenser, but my tach still drops to zero and bounces back up and down at high revs. Smooth and steady from 1000 to 4500, then, boom. falls right off as the car is still reving higher.
I also noticed that at any RPM, if i use my directionals, the tack also freaks out.
Almost like some electrical gremlin. I think all my grounds are good. Maybe I have bad bulbs that are causing feedback?? open to any recomendations

Is your tach to coil wire in good condition/ connection ?, it seems to me the tach may have a poor earth or worst of all the tach is failing which due to age (ask me how I know ) my 911 tach pretty much did what yours is doing before total failuure .
Worth checking all the wiring and maybe try a secondary tach to body ground wire and see what you achieve ? ,good luck cheers.
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moneysmarts
post May 13 2026, 04:38 PM
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Thank you
Is there a wire that runs from the tach through the tunnel directly to the coil?
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Freezin 914
post May 13 2026, 06:08 PM
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Voltage regulator??.
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dtmehall
post May 13 2026, 06:10 PM
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i believe that the answer to moneysmarts question is yes
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cgnj
post May 13 2026, 07:01 PM
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QUOTE(moneysmarts @ May 13 2026, 03:38 PM) *

Thank you
Is there a wire that runs from the tach through the tunnel directly to the coil?

Black with Violet tracer. I do have a few questions.
If your car is idling and you turn on the turn signal, does the tach still drop out?
Have you bypassed the MSD?
Download this fileEasiest electical diagram
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moneysmarts
post May 13 2026, 07:48 PM
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QUOTE(cgnj @ May 13 2026, 05:01 PM) *

QUOTE(moneysmarts @ May 13 2026, 03:38 PM) *

Thank you
Is there a wire that runs from the tach through the tunnel directly to the coil?

Black with Violet tracer. I do have a few questions.
If your car is idling and you turn on the turn signal, does the tach still drop out?
Have you bypassed the MSD?
Download this fileEasiest electical diagram


I just went outside and tried to duplicate while the car is idling, but I could not.
I have not tried to bypass the msd.
While driving though, the tack does drop momentarily when I use the turn signals.
The switch is definitely effecting the tack. And of course it doesn't change the rpms at all Just the tack reading.
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Spoke
post May 14 2026, 03:36 PM
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For the interaction with the turnsignals, try removing the tach turnsignal indicators from the tach; tape them up and run the car and see if the turnsignals still interact with the tach.
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dtmehall
post May 14 2026, 08:46 PM
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sorry to get outside of our main thought process...........

but i stumbled across this youtube about a similar problem.

which was solved by adding a resistor

hope it helps

https://www.youtube.com/watch?v=VA7J0KkanzM
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moneysmarts
post May 15 2026, 05:00 AM
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QUOTE(Spoke @ May 14 2026, 01:36 PM) *

For the interaction with the turnsignals, try removing the tach turnsignal indicators from the tach; tape them up and run the car and see if the turnsignals still interact with the tach.



I will try that today and report.
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cgnj
post May 15 2026, 05:54 AM
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@dtmehall Why would you post Indiana Jones movie clips in this thread?
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dtmehall
post May 15 2026, 07:03 PM
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sorry, i copied the wrong url

the video i saw suggested adding a 10k ohm 1/2 watt resistor to the signal wire from the coil to the tach
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cgnj
post May 15 2026, 08:52 PM
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QUOTE(dtmehall @ May 15 2026, 06:03 PM) *

sorry, i copied the wrong url

the video i saw suggested adding a 10k ohm 1/2 watt resistor to the signal wire from the coil to the tach

He is using a MSD 6AL. Tach doesn't connect to the coil. It is connected to the MSD 6AL.

It used to be that sometimes the MSD tach adaptor was needed to operate the tach. I have never observed that problem with both early and late tach. That is why I told him to disconnect the MSD box. Maybe the tach is or the MSD have changed over the years. Easier than pulling the bulbs out of the tach.
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Spoke
post May 16 2026, 09:00 AM
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Not sure what year your 914 is. For the '74 year the turnsignals and tachometer share the same fuse. The fuse is #9. If you haven't already remove the fuse and clean the contacts on the fuse (or put a new one in) and clean the contacts on the fuse panel.
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moneysmarts
post May 16 2026, 11:04 AM
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QUOTE(cgnj @ May 15 2026, 06:52 PM) *

QUOTE(dtmehall @ May 15 2026, 06:03 PM) *

sorry, i copied the wrong url

the video i saw suggested adding a 10k ohm 1/2 watt resistor to the signal wire from the coil to the tach

He is using a MSD 6AL. Tach doesn't connect to the coil. It is connected to the MSD 6AL.

It used to be that sometimes the MSD tach adaptor was needed to operate the tach. I have never observed that problem with both early and late tach. That is why I told him to disconnect the MSD box. Maybe the tach is or the MSD have changed over the years. Easier than pulling the bulbs out of the tach.



I pulled the directional wires from the back top two holes on the tach. No change.
Tach reading still drops off during acceleration when I use the directional lever.
My Msd wiring has never changed in 25 years.
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