I'll crosspost this thread to the GM Newsgroup. Someone there should know.
I'll crosspost this thread to the GM Newsgroup. Someone there should know.
All 4 headlights being lit was common back in the days of glass & metal headlight fixtures. Now, with plastic/plastic headlight fixtures, heat is the enemy.
One bulb on each side was a high beam bulb. The other was a 2 filament bulb, high and low. Therefore, all four were lit only on high beams.
Dave
And there are few vehicles that have that configuration any more, now being only two high/low dual filament fixtures per vehicle, or four headlights per vehicle, with discrete low beam outboards and inboard high beams. The official justification for the low beams going off when the highs were engaged was that high levels of foreground light from the low beams being left on with the highs diminished the effectiveness of the high beams, but I still think it's the heat from 4 bulb filaments burning at the same time in those plastic housings with plastic reflectors and plastic lenses.
You are probably correct that the plastic housings and reflectors wouldn't stand up to the heat produced by both filaments, but the old glass sealed beams wouldn't have had that problem, yet they only burned one filament at a time. I suspect filament life would be drastically reduced if both were on at the same time.
Dave
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.