It was actually the mid '70's, SlantSixDan just answered this one in another thread somewhere, cited FMVSS I believe '77 model year. ALL vehicles had to comply w/the
std. for that model year, or sell the car in another country. Yes, it is to not confuse a warning lamp You may have been ignoring, w/the hi beam indicator alerting You that
you are blinding oncoming traffic.