Ok finally found a tach I like and wired it in today. First off it looks great minus the red illumination. Hope I can fix that. Problem I have is it reading 200-400rpm higher than what my digital timing light says. Everything is all good and snug. Its wired direct to tach on hei distributor was I supposed to have a resistor inline? Any help be great.

 

No ballast resistor on HEI. Bad spark plugs, wires, disributor cap can cause high readings.

 

Finally, if it is an older unit that you bought from someone else used then it might need an adjustment. If there is no stop, does the needle read zero when the engine isn't running or does it drop lower than zero. If the reference is lower than zero then your error will be off by that much. Some tachs have an adjustment for that. Just a thought.........

 

Sorry the cap/plugs/rotor/wires/coil/module and wires are new. Tach was new in box. Only adjustment was choosing which cyl/pulse setting. Tach reads 0 when not running.

 

If you search here there a a few posts about repro tachs not reading correctly and a few posts on how to fix it (not that you should have to with a new one )

https://classicoldsmobile.com/forums...ation-how.html