Flickering / bouncing is almost never the VR unless it's the older mechanical one, but "it could be" in rare cases.
Next thing you need to do is check the bulkhead connector and check connections. Figure out the charge path from battery---through the bulkhead/ ammeter--and to the alternator. YOU MAY WELL HAVE modified wiring what was known as "fleet / taxi/ police" which ran the ammeter wiring through separate gromments in the firewall instead of the bulkhead connnector
Be ABSOLUTELY certain that the VR is well grounded to the battery You want these things well bonded together, and the larger the alternator and the more loads you have the better this must be:
Block, battery, frame, body and the VR all must be well grounded to each other. Don't be afraid to add larger cable.
CHECKING FOR VOLTAGE DROP. I've posted this a zillion times, but it is important
Check both the "harness" side and the "ground" side
1....Find ballast resistor, or as close as you can get to VR. Turn key to "run" engine stopped. Measure ballast to ground, find the highest reading which should be "battery." Stab one probe onto that and the other probe into the top of the battery POS post. You are hoping for a very low reading, the lower the better. Anything over .3V look for why.
I cannot tell you on that "rig" on a "stocker" the "general" path is battery..........starter relay big stud...........fuse link..........through the bulkhead (RED ammeter wire)............to and through the ammeter.........out on BLACK..........to the WELDED SPLICE under the dash...........branch off to igntiion switch connector............through switch........back out on "igntiion run" IGN1..........back out bulkhead usually dark blue...........to ballast.........branch off to VR and other underhood loads, alternator field...........smog equipment...........electric choke.........THAT VEHICLE MAY HAVE a "field loads" relay
2.....Check ground. Get engine warm, battery "normalized" and running on fast idle to simulate "low to medium cruise" RPM. Run this test first with all loads off, again with lights, heater, etc powered on
Stab one probe of your meter into top of battery NEG post. Stab remaining probe into mounting flange of VR. Be sure to stab through paint, rust. Once again, you are hoping for a very low reading, zero volts would be perfect
If you do all this and it won't settle down, run the thing at various RPM and various light and heavy loads while montoring the alternator output stud to the battery POS post. If your meter reads an absolute maximum of 2V under heavy load you are on the borderline. If that voltage jumps around while the load is "stable" you may have a bad connection in the charge line to battery. Also "rig" a heavy wire like no14 with a female "flag" push on connector to fit where the BLUE field wire is connected. Jumper that wire over to the battery GOOD connection. See if that settles it down. Note of course this is a test and not to be driven that way, as the alternator field will be powered / key off
Also re-check alternator for problems especially brushes and a bad stator, and replace VR
