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My Nova has a Pontiac hood tachometer, when I got the car it wasn't working. Someone had hacked a pigtail onto the factory wiring, so I cleaned that all up. The car also has a MSD box and I read that these tachs wont work off of the MSD feed, and they make a adapter box to fix this. I got the adapter box, got everything wired up . The internal lights come on in the tach, but it still will not read any RPMS. Is there any way to test this tachometer. I'm pretty savvy with wiring, so I'm pretty sure it's wired correctly. My electrical theory is a bit rusty though. If someone could walk me through how to basically bench test this tach to see if if it's good or bad. Thanks for the help. FYI there are 3 wires coming off the tach side (Tan/Purple/Black)
 

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To bench check it, you will need a 12V DC power supply and a signal generator. I tested a factory indash tach for use in my 74 years ago with a signal generator we had at work and I cannot remember how much voltage was needed nor do I remember if I was using a square wave output or a sine wave but a good tech may be able to tell you the settings needed.

Maybe think about wiring the tach onto another older car and see if it works.

Who knows there may be a cold solder joint inside, a burnt part or circuit board trace, or possibly even a capacitor or two that might have dried out or gone south.

Jim
 
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