New Owner from Michigan

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bbodie52
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Re: New Owner from Michigan

Post by bbodie52 »

In the tachometer schematic, the square wave on the left simply indicates the on/off switching that is occurring on the coil negative terminal each time the ignition points open and close. The tachometer senses these on/off pulses via the brown wire on the negative coil terminal and counts the pulses. (The black wire that is also connected to the negative terminal is wired to the ignition points. When the points are closed, current flows through the coil primary coil winding — which builds up an electromagnetic field. When the points open, the electromagnetic field collapses, which induces a spark voltage in the coil secondary winding — sending a spark voltage to the spark plug). The pulse count is translated by the tachometer circuit into a needle deflection — which is displayed in engine RPM.

In addition to the Brown tachometer sensor wire, there is another wire (20 B/P) that provides 12 VDC to the tachometer internal electronics to power the tachometer. You should be able to measure a continuous 12 VDC at this connection whenever the ignition key is ON. The ground return to the battery is chassis ground. A good ground on the ground strap shown in the instrument panel back side illustration is critical for the proper operation of all of the electrical instruments (tachometer, cylinder head temperature, fuel gauge, and clock. The instrument panel structure itself is plastic, so the metal point-to-point ground strap, which is connected to the dashboard frame, is the only source of the instrument panel grounding.

The original wiring diagram in the shop manual has the wires crossed at the two-wire connector shown at the top. This was an error. The Brown sensor wire passes through the connector to the BRN/W wire and on to the tachometer input.

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1965-66 Corvair Instrument Panel Detail (Corsa).jpg
1965 TACHOMETER WIRING
1965 TACHOMETER WIRING
1965 TACHOMETER WIRING
1965 TACHOMETER WIRING
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
gcjacobs
Posts: 14
Joined: Tue Oct 25, 2016 5:39 am

Re: New Owner from Michigan

Post by gcjacobs »

Thanks Brad...the schematics are great. So based on what you said and what I see in the schematics it looks like I have the brn/w hooked up correctly. I am getting power to the b/p wire so kind of thinking when they re-wired the car they hooked up the tach based on the shop manual which has those wires switched (so the tach is going to my cyl head gauge and vis-versa). Going to look tonight...hopefully that is the case, and this will fix both problems...thanks again!
Greg J
Rochester Hills, Michigan
1965 Corsa Convertible
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bbodie52
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Re: New Owner from Michigan

Post by bbodie52 »

Don't forget to verify a good ground connection at each instrument pod. The ground strap must have a secure connection to the dashboard, and it travels from point to point to each metal pod. Voltage input without a good ground return would result in a non-functioning, tachometer, cylinder head temperature gauge, faulty fuel gauge operation, etc. The speedometer and vacuum gauge are mechanical and do not require power to operate. The clock usually doesn't work on Corsa instrument panels anyway, because they were pretty unreliable.
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
gcjacobs
Posts: 14
Joined: Tue Oct 25, 2016 5:39 am

Re: New Owner from Michigan

Post by gcjacobs »

Wanted to thank Brad (bbodie52) and BobWitt for the diagrams and the suggestion to look at the coil...sure enough the brn/w wire was on the positive side, switched it over and the tach is now working
Greg J
Rochester Hills, Michigan
1965 Corsa Convertible
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