Charging circuit issues

[CutterN55]

I go out to start the truck yesterday evening as we get ready to go to church and the Batt light is on flickering (more on than off) at idle, door open lights are really flickering, and the battery guage is all over the place (down to as low as 8 and as high as 18-20). I didn't drive it and am about to go to parts store this morning.

CHanged parts:
2 Optima Red tops within the year
new motorcraft belt and tensioner 3-4 weeks ago
battery connections are clean & solid.
Alternator new from Orielly's about 2 years ago & wasn't a cheapo.

This has been going on occasionally for a while (before alt swap) but not near this bad where I didn't want to drive it.

[CutterN55]

Regulator was bad intermittantly. Also replaced the positive battery harness for good measure, was swollen in a few spots due to corrosion.