Well, Ive seen this posted countless times and never seen an actual fix before so I figured I'd post it again for all to see and see if fresh eyes can find a fix.
My 1992 325is's lights (all of them) flicker quickly when the engine is running. Its a pulsing or throbbing that all the lights experience.. backlights of the gauge cluster, obc, interior lights, headlights, brake lights, tail lights, etc..
the flickering is going on at any speed, and doesnt appear speed sensitive.. @idle or cruising in any gear.
Ive seen this problem alot and people try replacing batteries, alternators and neither fixed the issue for them. They never follow up though with how/if they did fix it after trying those though.
One thing: the lights all work normal when the engine is NOT running but running solely on the battery. Dont appear dim or anything, just normal..