My '88 300e has the unusual property of flickering or 'pulsing' of all lights, interior and headlights, at a subtle amplitutde yet at a constant frequency. id almost swear it affects the rpms of the engine itself, though its so minor in effect. the battery is charging, and the car runs fine.
I did a search on flickering lights here, but the issues concerned specific equipment, not a 'system wide" scenario. Ive checked the obvious, loose wire, changed fuses, etc.