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Pontiac Forum: RPM Gauge not working
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  #1  
Old June 6th, 2018, 02:40 PM
Nexia86 Nexia86 is offline
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RPM Gauge not working

Hello from Germany,


the RPM gauge of my 1969 Gran Prix is not working. I crawled under the dashboard and could see that there are only two wires coming out from the gauge: one which is connected with TACH of the HEI distributor and another one which is connected to battery/ignition. I was missing a cable which should be on ground - or am I wrong? Does anybody know if I can remove the gauge without removing the complete dash board?

Thanks a lot for your advise.


Regards
Manuel
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Old June 6th, 2018, 03:36 PM
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melsg5 melsg5 is offline
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To start with HEI did not exist in 1969 so somebody changed something if it is HEI.
You may be able to remove the gauge by dropping any AC ducts under the dash and removing the retaining screws for the gauge.
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Old June 6th, 2018, 03:51 PM
Nexia86 Nexia86 is offline
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Apart from the fact that it's not the original distributor, shouldn't there be a wire connected to ground? Can I get the RPM pulsation from somewhere else than from the distributor?
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Old June 6th, 2018, 05:17 PM
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the rpm signal has to come from the distributor.
did the tachometer work when you purchased the car?
the tachometer has lights with a single wire also, the housing should be grounded.
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Old June 7th, 2018, 06:46 PM
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Also if the Tach is original to the car it was not rated for the amperage the HEI Dist. puts out. If not modified the HEI will burn out a tach designed for a points ignition system.
If I remember correctly the Dash Tach grounds out to the dash mount itself. Thru a jumper on the back of the tach.
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Old June 12th, 2018, 08:32 AM
Nexia86 Nexia86 is offline
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Well, I believe the issue here is that the stock RPM gauge is not capable of the signal the HEI distributor is sending...

How can I make this work??
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Old June 12th, 2018, 11:54 AM
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you need to install a tachometer filter similar to this
https://www.corvettemods.com/C3-C4-C...iABEgJfwvD_BwE
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Old June 13th, 2018, 02:59 AM
Nexia86 Nexia86 is offline
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Found this one and Waiting to arrive:

https://www.glowshiftdirect.com/hei-...signal-filter/
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Old June 20th, 2018, 02:39 AM
Nexia86 Nexia86 is offline
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OK so I installed that filtre but it didn´t help. Maybe the gauge was already burned by the high voltage of the HEI...

How can I check that? To remove the gauge I need to uninstall the complete dash I believe?
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Old June 20th, 2018, 09:41 AM
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use a voltmeter to determine if you are getting a signal from the Tach terminal of the HEI. If you have to pull the tachometer you drop the lower AC ducts, remove the radio and support bracket, disconnect bulbs and power feed. Loosen the 3 retaining screws rotate the tachometer in a clockwise direction and remove. Those are the instructions from the 1970 factory service manual. Good luck.
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