Corsa Tach Not working

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rnd5553
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Corsa Tach Not working

Post by rnd5553 »

Got a Corsa IP cluster in my 66 Monza, but the tach is not working.

I have the power from the coil going to the proper pin location on the dash harness wiring connector, and it is getting power. When I shut off the engine the tach's needle moves a bit, but there no reading when engine is running. The dash is grounded via the factory IP ground location on the bottom.

I did table check the tach prior to install and it checked out ok.
I used the factory pin connector from an extra dash, and ran a wire from the negative side of the coil, and up to the wire harness dash connector.
Do I need to add power?
Looking at the wiring diagrams I should be good to go, any ideas?

Thanks
66vairguy
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Re: Corsa Tach Not working

Post by 66vairguy »

I assume you used the Corsa cluster harness and plugged it into your Monza under dash harness. The tach input requires adding another wire as you indicated you did. The power comes from the same wire used by the Monza cluster. If the fuel gauge and warning lamps work then you have power.

If you tried to used the Monza instrument cluster harness on a Corsa instrument cluster - well that would take a lot of work by a knowledgeable person. You'd be better off just ordering the correct wiring harness for a Corsa instrument cluster.

The tack only has two connections, power and coil, that are marked on the rear housing. The case grounds via the gauge ground strap that is needed since cluster housing is plastic. Did you screw the ground strap to the tachometer gauge case when you installed it?
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bbodie52
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Re: Corsa Tach Not working

Post by bbodie52 »

The signal sense lead for the tachometer is a Brown (20 BRN) wire that attaches as a second connection to the negative terminal of the ignition coil. (The other wire on the negative coil termanal is a short Black lead that connects to the ignition points in the distributor). The Brown (20 BRN) wire simply allows the tachometer to count the on/off pulses as the points open and close. The number of on/off pulses is interpreted by the tachometer and translated into a calibrated gauge meter deflection, which is displayed as RPM.

There is an error in the shop manual schematic at the top of the first wiring diagram. The Brown (20 BRN) wire crosses a two-pin connector and exits on the other side as a Brown wire with a White stripe (20 BRN/W), which continues and passes through a 12-pin multi-connector, which is then routed to the tachometer. The other wire, labeled 20 B/LG, is the cylinder head temperature gauge wire which goes to the left cylinder head sensor.

The tachometer power is provided to the tachometer by the 20 B/P wire. The electronic circuit board inside the tachometer will not function unless there is a GROUND return path for the voltage that is supplied to the tachometer. This ground path is provided through the tachometer metal case, and is routed through the instrument panel ground strap system that has to be physically attached (by a single screw) to the instrument panel dashboard frame. Be sure that you have a good ground attachment at each instrument cluster, and at the instrument panel to dashboard frame. All of the electrical instruments (fuel gauge, cylinder head temperature gauge, clock, and tachometer) must be properly grounded. The mechanical instruments (speedometer, vacuum gauge) do not require power or a ground connection.

Left-click each image to enlarge for better viewing...
1965-66 Corvair Instrument Panel Detail (Corsa).jpg
1965 TACHOMETER WIRING (1).jpg
1965 TACHOMETER WIRING (2).jpg
Wiring Circuit Color Code.jpg
:chevy:
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
Scott V
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Re: Corsa Tach Not working

Post by Scott V »

the tach has 2 connections on the back.

coil negative.
12+ . this is not power from the coil like you have it. you need 12 volts.....something that is switched key on/off.

make sure the tach is grounded.

-Scott V.
rnd5553
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Re: Corsa Tach Not working

Post by rnd5553 »

Ok so Brad, you're saying the connector (wire) from the coil should be in the last position on the Corsa's IP cluster's harness wire connector, and NOT in the second to the last position ( on the connector) that exist to a pink wire going to the temp gauge per my 1966 Corsa IP diagram.

You're saying to insert the wire connector running from the coil in the LAST position on the dash's connector, so it's exits to the BRN/W wire that looks like it goes to the Gen Fan Indicator on my diagram. Is this correct, thank you.
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bbodie52
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Re: Corsa Tach Not working

Post by bbodie52 »

I tried to clean up and combine three 1965 schematic wiring diagrams to clarify the tachometer connections. In this image I eliminated the instrument panel wiring for the Monza, and only show the Corsa instrument panel details. If you left click on the diagram below it should enlarge the view so that you can see it more clearly. Also, the wiring color codes may have changed in 1966. The connections will be unchanged but the wire colors may not be the same as they were in 1965.

The ignition coil and tachometer are highlighted in blue. If you locate the tachometer you will see a wire labeled 20 B/P. This is the tachometer power wire that provides the internal electronics with 12V DC whenever the key is ON. This wire can be traced back to a central junction point in the wiring harness. You will notice that many instruments and warning lights are all tied to this junction point, and all of the wires are labeled the same (20 B/P). This provides all of the instruments and warning lights with power that is switched on when the key is in the ON position.

All of the lights and electric gauges are grounded through their metal housings.

The other wire that is connected to the tachometer is the signal sensing wire that can be traced to the negative terminal on the ignition coil. On the 1965 Corvair this wire is labeled 20 BRN/W (20 Gauge Brown with a White Stripe). The color may be different on the 1966 Corvair. This wire passes through a 12 pin multi-connector and exits the other side with the same color code. It then routes to a two-wire connector that is not illustrated correctly in the shop manual diagram, but I have added lines to the drawing to try to clarify the connection at that point. The wire remains Brown after it passes though the two wire connector, but it loses the white stripe. If you trace the 20 BRN wire it runs to the engine compartment, and you will see that it passes through another 12-pin multi-connector in the engine compartment and continues on (still 20 BRN) all the way to the ignition coil negative terminal.
...You're saying to insert the wire connector running from the coil in the LAST position on the dash's connector, so it's exits to the BRN/W wire that looks like it goes to the Gen Fan Indicator on my diagram. Is this correct...
In the 1965 wiring diagram, the tachometer signal sense wire is adjacent to an empty (unused) hole in the 12 pin multi-connector and is the second pin down. The third pin down is the B/LG wire that goes to the cylinder head temperature gauge.

If your tachometer proves to be wired correctly, has 12V DC fed to the correct connector (key on) and is properly grounded, and the signal-sense wire is properly wired to the ignition coil negative terminal, and your tachometer (which you indicated functioned properly when it was bench checked out of the car), still does not work, the other possibility for a fault lies with the multi-connectors — particularly the multi-connector in the engine compartment. This plastic connector is subject to age, moisture, heat and vibration, which can produce faulty electrical connections between the metal pins inside the connector. You may have to separate the two halves of the plastic connector and check the metal contacts inside for corrosion or other damage that could be interrupting the connection between the tachometer and the ignition coil. A multimeter should help you to confirm electrical continuity in the wire between the coil and the tachometer.
1965 Corvair Tachometer Wiring.jpg
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Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
rnd5553
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Re: Corsa Tach Not working

Post by rnd5553 »

Close - after all this found that my tach was defective, got new one, works fine. Thanks to those that responded.
66vairguy
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Re: Corsa Tach Not working

Post by 66vairguy »

Don't throw the old tachometer out. A buddy is working on a kit to add new internals, but you have to use the old dial face and housing.
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Canadian3Fan
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Re: Corsa Tach Not working

Post by Canadian3Fan »

66vairguy,
Did your buddy develop a tach rebuild / replacement kit?
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