Messing around with the headlights on my father's '86 GL this week, I
measured 11.3 volts at the headlights (with the engine off).  Out of
curiosity, I added a new ground wire to each headlight assembly and lo &
behold, the voltage was now measured at 12.35 volts (engine still off).
Headlights were quite a bit brighter.  Cheap and quick help for common
problem.  Just thought I would pass it on.

Cheers,

Jeff