I have a 2002 Dodge Neon SXT with about 72050. One day I started it up and the gauges started jumping up and down like you were turning it off and on. All lights on the instrument panel and the interior if they are on will flicker from bright to dim and so on along with the gauges. It doesnt seem to bother any other electrical components. Power windows work fine along with everything else except for the gauges and interior lights. I can be listening to the radio and the clock and lights just go off and on and bright to dim, but the radio stays on. Sometimes it does it as soon as I start it up and sometime after I have been driving. Sometimes it will go back to normal for a little bit then start going crazy again. After its been doing this for awhile the gauges will just move slightly. The odometer will be showing like 72010 and then 72009 or whatever the milage is at that time when it going off and on.
to check your alternator, start your car, then while it's running, pull off the positive terminal from your battery. If your alternator is good, you should NOT notice a change in the idle speed of your car. If your idle speed suddenly drops or you car dies all together, your alternator is shot.