Flickering can be caused by a several issues. WTF are you working on? What year? Does it have the older 69/ earlier mechanical regulator -------or are you trying to say it's a 1986?
Bad connections/ terminals in the charging line / path from the alternator to the battery.
Bad ground at the regulator
Harness drop/ bad connections in the harness supplying power to the regulator.
As stated, something wrong in the alternator INCLUDING BAD BRUSHES
WAY WAY back in the 70's a friend had a 69RR and it flickered and wobbled the ammeter BAD. Turned out to be a BAD WELDED SPLICE---this is the one in the black ammeter wire up under the dash.
