A significant improvement can be made to the performance of Mercedes 126 headlights by replacing the DOT-approved units with genuine European headlights. There is also a major aesthetic benefit.
Particularly in the case of the early (first-generation) 126 cars prior to 1986, the DOT-approved headlights for the US market were horribly inefficient compared to the Bosch lights installed in Europe. The pun is barely excusable, but the difference in light output is almost night and day. One can only assume that this lamentable state of affairs was the result of federal regulations drafted at the behest of certain congressional chairmen protecting the commercial interests of businesses within their districts. The rules increased demand for traditional, sealed-beam headlight units at the expense of road safety.
Genuine H-4 "Euro" lights are still available new from Bosch but are very expensive. Fortunately, good used units can be found both domestically and from European sellers. And there are after-market copies from companies like Depo which look almost as good (but are not as well made). The glass lenses can be bought separately in the event of damage, but internal parts are no longer sold separately.
In addition to a superior reflector and lens design, Euro lights offer the Mercedes owner the flexibility of easy bulb changes without replacing the unit unit. And the performance of the lights can be enhanced even further with high-output or over-wattage bulbs. Having said that, one should be leery of imposing an excessive load on the wires to the lights. While Mercedes wiring is better than most, there comes a point where excess heat could damage the wiring and voltage drops would impede performance. These problems can be obviated by employing relays. But for most drivers, the output from the standard European bulb will be more than adequate.
European headlights also offer a city light – a small, 4-watt bulb which can easily be wired up to the existing circuit for side-marks, providing additional forward identification. And for gadget lovers, there is a vacuum-driven height-adjustment feature which can be used to adjust the lights from inside the car when carrying heavy cargo. Some understanding of the car's vacuum circuits is needed for this modification, but it is not difficult.