A Guide to Bosch H1 Headlights | Audette Collection: The Definitive Resource on Vintage Porsche 911 Lighting
"Did you know that Bosch H4 headlights for 1972 and 1973 models are different from all subsequent H4's? Unlike subsequent years they don't have the small 4w city light in the reflector as those are in the front turn signals. As a result they have a different bulb holder from other years. And for some unknown reason they also have a different shield that is riveted unlike other years."