[Tigers] AutoMeter Cobra 8000 Tach installed

[wsamouce]

Much Thanks to Paul R. Breuhan [prbreuhan at hotmail.com] for his screening
services, I now have an accurate 8000 tach in my Tiger.

http://i796.photobucket.com/albums/yy249/samouce/002-5.jpg

http://i796.photobucket.com/albums/yy249/samouce/004-1.jpg

I used the original gauge's class, outer and inner bezel too. This takes
about 1 hour worth on modification to the autometer's case. 

Now a question for you all - 

I am having a problem with the needle jumping around when the engine is at
idle.  Once the rpm is over 2000, it reads correct.  When I turn on the
lights, at idle, it settles down a lot but still twitches.  Sometimes when I
start the car it read the correct idle for a few seconds and then starts to
jump.  I called the AutoMeter tech line and the guy thinks that I have a
ground or 12v power issue.  He suggested that the alternator may have a bad
diode and is causing voltage problems at idle.  I tried using different 12V
sources with no fix.  I also tried different grounds with no success.  

I am also using a accell electronic ignition kit in my distributer.

When driving the car, the tach works perfect......until it drops to idle.
Any advice as where to start?

Duke 
B382002037