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I bought my 71 and the guy said the Tach did not work so I researched the forum and here is where I am at:
1 -- The blue and black strip "pulse" lead was on the 12 volt supply pole.
2 -- The Blue and White 12 volt supply wires has 1...the Blue( No white there )and it was on the pulse pole.
3 -- Ground is 2 black and on correct pole.

This is all from this picture that was on a thread with a good shot of the back of the Tach and the correct wires to the correct poles. I ran a test wire from the negative on the coil around the door to the Tach and put on the pulse pole. At idle it reads 5.20 volts and when you rev the engine the reading goes up to about 11.something....maybe higher but I didn't get stupid. Any thoughts? Wonder if the internals of the Tach are damaged due to the 12 volt supply being on the wrong pole? While we are here...where should I send Tach and Speedometer to get the once over? (Speedo reads wrong and noisy) PS. I am in Canada
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Jon Haas of Pantera-electronics went through mine for me. Actually two of them.

Good thing too. They were both pretty sick.

Something about the entire internals of these tachs being one large printed board? Forgot. Ask him. He'll know?

Contact him at jhmotorwerke@gmail.com. Tell him I sent you.

Ask him about the speedo though. I don't know if he can do much for it?
Inside the tach case is a small circuit board driving the needle, that among other parts holds a couple of all-glass precision resistors. On one car, a glass resistor had cracked in two and needed a microscope to even see the crack. I found that if you replace the 2% resistor with one (or more) even slightly off in value, the repaired tach won't read correctly and there are no built-in adjustments. Commonly available resistors are 5%, 10% or even more. Not a job for a rookie EE like me...

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