Gauges gone haywire! Options

[BfloRandy]

Hello everyone, I have enjoyed reading many of your posts this summer. I finally got myself stuck, so here is my issue, hope someone can help!

I have a 75 2.0L. I'm getting the "G" light (alternator?) on and the gas gauge and tach are going screwy. Sometimes, they work normally, and the light is off, others, the gauges fall to zero and the light is on, others still, the light will be on but dim and the gauges sorta work, for example I know I'm over 3k RPM, but the tach is showing 1400. When I even touch the brakes, the G light comes on and the gauges die, returning sometimes when I let off the pedal. From what I have been able to find, this sounds to me like an intermittent ground perhaps. I have also seen that it could be an issue with either the voltage regulator or the alternator itself. This issue just came out of nowhere today, it has not been a gradual onset thing. Am I correct in assuming that it has to be a sudden catastrophic failure in the reg or alt or even something as simple as a ground wire just popped loose? The car runs just fine. The speedometer works normally.

Any help or ideas would be immensely appreciated!