run a ground wire from - side of Batt to the VR mounting bolt.
might have a good look at the fuseable links while you are at it. any of it soft or discolored.
if it has the dimmer on the floor,check those wires at the plug,the will brake and cuase trouble with the headlight.
it could be as simple as adjusting the curb idle up on the carb.
both my trucks dim at idle but it is from a low curb idle setting of 650rpm.
the flicker part could be a problem. resitance in the wires or bad grounds.
my buddys 85 fury had a charging issue and poped 2 set of headlights. not sure if he got it fixed though he did park it. it was a regular 65 amp alt set up.
my 85 poped 2 set of headlight till I patch up the fusable links for headlights and ign. IIRC my radio smoked it or got smoked on the 2nd set of bulbs.
got any spare bulbs just in case?
