I assumed that this was the case, and that the bouncing tach I have been experiencing was caused by my alternator being on its way out. To confirm this, I went to the auto parts store up the road (Advance Auto Parts) and had them test it. They reported that it was fine and gave me the results, which were as follows:

No Load: 15.20 V / 0.2 A
Load: 14.84 V / 0.2 A

My battery also checked out just fine at 13.17V and 845 Cold Cranking Amps.

If you were in my shoes, what would you do next? Second opinion on the alternator test? Replace it?

 

I have had parts stores test starters and alternators that tested fine, but didn't work.

An erratic tach is one of the first signs of a bad alt.

 

It doesnt look like they loaded up the alt for ampere output just voltage. Its possible the alt can make sufficient voltage but not enough amps. But the tach draws minimal amps so i doubt thats the case. Does the tach always jump around? Try turning on high amp circiuts like the defroster grid, seats, fan on max and see if when you do there is a direct effect on tach movement. Outside of that I personally would pull the cluster and be looking for a funky ground in that area.

 

Check for loose wires on the back of the alt.
Then get a second opinion.

 

Thanks as always for the help gentlemen. I pulled the wires off the back of the alternator and sanded them to clean any corrosion, although I didn't see any, and did the same for the battery terminals and it seems to have solved the problem for now. I'll report back in the event that the gremlin returns.

 

That was the problem on mine (daughter's) even with the new alt replaced due to a growling bearing. White wire connector needed cleaning. Works good now.