I have a 69 Cutlass and had purchased a NOS tach on Ebay for a 70-71. I figured I could make it work. The casing is where the difference is. I took the internals from the new one and mounted them in the old clock enclosure. It works but something is not right. When the key is off the needle rests at 0, when I turn the key on it jumps to 200 before I start the engine. I never knew if it was just that difference or off more than that. So I purchased a steering column mount tach and wired it up and that seems to be the difference. Any thoughts on what would make it do that?
thanks
Steve

 

These tachs weren’t very accurate when new. Make sure you have a good ground. Other than that, it might just need rebuilt/recalibrated.

Dors the clock work? If not, get the quartz conversion at the same time. It’s too much of a hassle getting the gauges out of those cars to do it twice.

 

Curious, when you said a NOS tach from ebay. Was it a reproduction or a genuine NOS?.

 

Genuine, in box. I don't recall exactly but it was about $100
Steve

 

You got a good deal Steve !.