tachometer acting unhappy

[Godsmack635]

my factory tic toc tac in my '68 Charger was working fine until I fixed an overcharging problem.  After picking up two new alternators and finding both were shorted out, i finally got a third alternator that was good and installed it along with my new voltage regulator.  I had all three alternators tested before I left the auto parts store and was told all were working correctly.  My charging system is working as it should now but i noticed my tach only goes up to 2000 rpm on the freeway when it used to read 2600.  Any idea what could cause this?  There were a few people messing around with wires at the alternator as we were trying to figure out the overcharging of the electrical system.  Not sure if someone touched a field wire where they weren't supposed to or what..............Any help is appreciated.  Thanks!

[A383Wing]

tachometer gets its signal from the "negative" side of ignition coil.....changing the alternator should not have done anything to the tachometer system.

What kind of ignition system you running?

[Godsmack635]

MSD 6AL ignition system.  tach was working fine until we spent a weekend swapping out alternators and voltage regulators. 

[Ghoste]

And it worked with the MSD before?   The MSD isn't a recent add-on without the tach adaptor is it?

[Godsmack635]

No it isn't.  It's the same MSD that's been working with the car since i bought it. 

[Ghoste]

 

[Godsmack635]

Sounds like its time to pull it and have it sent out for re calibration.  Been entertaining the idea of having the entire instrument cluster reconditioned.  Thank you for all your help guys I appreciate it.