Both of the following sites will have good wiring info. You really don't want to wire them directly to your hibeams - extra load! It would be better to have the hi beams trigger a relay that switched on the Hellas when your hibeams came on - minimal extra load, and much brighter driving lights without that burning insullation smell. If you run the regular headlights and hi beams off of heavier wire and a relay as well, they will also be brighter.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E