68 Barracuda........ Temp and Gas Gauge Issue.

If your AM radio is working, tune to a spot where the band is silent, and you should be able to hear the ticking about once a second, sounds almost exactly like when you are listening to a weak signal and driving on a road with an electric fence alongside.
It's even visible on some cars' ammeters.
In my '71, I put in a 5 volt solid state regulator, to get rid of the AM radio ticking, which capacitor bypassing did not seem to help. Unfortunately it creates more battery drain than the factory regulator.
Not much, but for sure.
My '72 Dart seems to have a "smoothed out" ammeter; the pulsing is only visible if you look VERY closely, and I'm looking right now with ign turned on.