Tachometer just twerking

[manofsteel]

Tanned new wire from engine to tach but it still will not work. Changed polarity on coil but still nothing. At least when on one of the polarities it twerked once in a while or while either starting or turning off engine? Does that mean the tach is no good? Can it be sent somewhere and get fixed? Let me know

[bbodie52]

Like a dwell-tachometer test meter, the tachometer in the instrument panel is designed to sense the on/off switching at the ignition coil negative terminal. This switching occurs when the ignition points inside the distributor open and close, which switches the ground at the coil negative terminal to turn the coil on and off.

For your instrument panel tachometer to function, it must be powered ON when the ignition switch is in the ON position, The tachometer must also be properly grounded so that the internal electronic circuitry is provided with power and a ground return connection to the battery. The sensor wire connection to the coil negative terminal is a trigger that allows the tachometer circuitry to count the on/off pulses at the coil, and translate that count to a meter deflection of the tachometer needle to give you an RPM reading that is calibrated for the number of cylinders in your engine.

You must check the tachometer wiring to ensure 12 VDC at the power connection, a proper meter ground connection, and a good signal connection to the ignition coil negative terminal.


Corsa instrument panel alternatives...

viewtopic.php?p=123415&hilit=corsa+ground#p123415

The Corsa and Monza instrument panels can also develop problems with the electric instruments. The panels are plastic, so a metal conductive grounding strap links the electric gauges together and then ties them to chassis ground at a single point. If the single screw that attaches that grounding strap to the metal dashboard becomes loose or corroded, the electrical ground to the instrument panel components may be lost and this can disrupt the operation of the electric gauges and illumination lights.

If you follow the tachometer circuit, you will note several wiring connectors in the circuit path. A loose, faulty, or corroded connector in the tachometer sensor wire path could disrupt the tachometer operation. You should use a multimeter to confirm electrical continuity from the tachometer connection to the ignition coil (20 BRN/W >> 20 BRN). A multimeter can also test for instrument ground and power at the tachometer (20 B/P).

1965 Corvair Tachometer Wiring

Left-click the image two times to enlarge to maximum enlargement , for better viewing.

[66vairguy]

I used to repair the LM tachometers. Mostly for myself and club buddies. I STOPPED doing it. Another fellow name Craig Nicol was also doing them and he also stopped. The electronics are easy to fix. The meters are NOT.

There were three different types of meters used with the same circuit board design (actually two different circuit board designs, but form and function is the same). The meters that drive the needle were well built laboratory quality and I suspect no one vendor could meet the demand - so three different types THAT ALL WORK THE SAME! Only one type has a problem that is easy to fix - the other two are next to impossible to fix. All the meters have one issue that makes them unrepairable ---- eventually the armature (needle shaft) springs fail and CANNOT BE FIXED as the parts are unobtainable.

I'm not exaggerating when I say they are like working on a watch mechanism - very fragile, precision devices.

IF YOU REPLACE THE TACHOMETER - DON'T THROW THE OLD ONE AWAY. I've been asked to do a modern upgrade to repair old tachometers. It's probably not going get done until later this year, but initially it looks good.

[acarlson]

I may have the tach from my '65 Corsa sitting in my parts box. I believe it worked when I took it out - I can't say if it still does. You can have it for free, just pay the shipping. I'll just need to find it