RPM Gauge not working

Nexia86

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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
 

melsg5

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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.
 

Nexia86

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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?
 

melsg5

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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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cammerjeff

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Belleville MI
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.
 

Nexia86

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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?
 

melsg5

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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.
 

Nexia86

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Gentlemen,

me again - finally I tried to get the gauges out of my car. It was a big mess to do but here we are.

I have attached a pic of the tachometer and the speedo. The tach didn´t work, I found out that the black wire coming from the bulb socket was not attached to the tachometer. Does the wire has to be connected to the screw marked red? WIll this make the tach work again? Can I test it without running the engine?

Regarding the speedo, the lamps didn´t work at all (bulbs were ok). I believe the printboard is completely gone, everything is loose - do you agree? Is there anything I can do to restore this or do I have to get a replacement? Is there any source you know where I can get such an aftermarket printboard?

Thanks,
Manuel
 

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melsg5

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concerning the circuit board, www.amesperf.com sells them. Concerning the wire, do you have the 1969 shop manual and looked at the diagrams in the accessory section for the tachometer?
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Nexia86

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OK I checked the shop manual and it´s a bit confusing. I believe the car was delivered with a clock instead and the tachometer I have removed is an aftermarket part and replaced the clock. The stock clock (or tachometer) had a metal housing and the ground strap was fastened to the housing. Now the tachometer I have got a plastic housing. So the question is, where should I put ground to? I made a picture of the inside as well, also I have the diagrams attached. Thanks for your help.
 

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melsg5

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if you have an aftermarket tachometer there are typically 3 wires. One to provide power to a illumination bulb for the face of the tachometer, another for the signal which is connected to a wire you have to run to the negative side of the ignition coil or if you are running an HEI to the TACH terminal of the HEI. The last wire would be a ground which can be attached to anything metal behind the dash.
 

Nexia86

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This housing has the holes to put in the stock light sockets, so we´re fine for the illumination. The two wires coming currently towards the tachometer are brown (TACH) and orange (12V). Just ground is missing. I think I will have to do some tests with a running engine and see. Is there a risk of blowing the unit?
 

melsg5

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seems to me the housing is grounded when the unit is installed in the dash. The diagram on page 15-11 only shows the signal feed and the light bulb feed. You can test it by grounding the housing with a wire and running a wire to the Tachometer connection.
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Nexia86

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It was already installed when I bought the car but it never worked. I can´t find a brand or anything on the tachometer so I don´t have any instructions. I will do some test and see how it goes...
 
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