Lights flicker and gauge jumps around???

How much of your under-dash wiring is factory? This sounds a bit like a failed splice in the ammeter wire. This is the factory splice in the black ammeter wire which feeds off to the headlights, ignition switch, fuse panel, and a couple of other things depending on the year/ model

It's a few inches from the ammeter in the black wire up under the dash. Only way I know to check it is to take some measurements and try to isolate it, then tear into the dash and physically inspect it

If you have not, and sounds like you have, read the MAD article which has a good simplified diagram

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

THANK YOU!!!! for posting relevant information.