Are aftermarket hood tachs adjustable?
 

My hood tach on my '67 seems a bit off. Seems to be reading too low. Are there any adjustment on them? And if so, can it be adjusted while mounted on the car or will I have to take it off the hood?

I recall when Padgett was repairing tachs, he used a graphite pencil to apply some graphite to a spot on the circuit board to tune the resistance. He said the factory reading was generally 200 RPMs off to read higher than actual engine speed. I do not recall where or how exactly but he had a meter reading the resistance and I saw it change to his desired spec.

This was close to 40 years ago and he's been gone 3 + years already. I did not commit the technical details to memory, obviously.

Hopefully someone else here has this knowledge.

And maybe this question would get more engagement in the Electrical forum.

Yes, the aftermarket ones usually include a potentiometer. You will have to remove the tach and unseal the top and bottom

Ok, thanks. I will give it a shot before I put the car away for the season.