Lights flicker and gauge jumps around???

wow , lots of ideas , this is similar to your lights and amp gauge issues , just ended up replacing my volt regulator with a adjustable one , just installed it turned everything electrical on for the load . and you must keep the case grounded to your running car . and adjusted right out , put a few amps of charger over the loaded unit . that was it for me , but you should also check the main charge loop goes into the car to the dash then to the battery , it could have an issue at the bulkhead connectors . hope you get it fitting my drove me crazier bright to dim .