Y07_A66:

The analog gauge may show fluctuations that the digital gauge does not, depending on how the digital gauge is making its measurement. For giggles, you could connect your digital gauge probe to the same wire going to the analog gauge.

What is the rate of fluctuation of the ammeter? Does the gauge spend about the same amount of time in either position, or does it spend more time in one of the two positions?

Is the behavior of the ammeter fluctuation similar to sound of the turn signal flasher? If you want to try a wild experiment, remove both flashers (turn signal and emergency) and disconnect the black wire from the back of your temperature gauge and see if the problem still persists.

This is a wild guess but to me it sounds that there is a high resistance short on a voltage wire that turns on and off (hence the change in current draw seen on the ammeter). I believe there are 3 such things in your dash: your 2 flashers and the voltage "regulator" for the instrument panel. Granted, the flashers should not typically be energized, but let's be cautious.

Dave