Originally Posted by Jeremy5848

Sorry to use a big word. The "combination switch" runs the turn signals and high-low-flash of the headlights. It is located in the steering column of all recent M-Bs including yours. The headlight wiring goes through that switch. It's unlikely to be the problem but you gotta check through the entire system, especially if the obvious stuff (fuses, sockets, bulbs, etc.) doesn't pan out.

BTW, I and others have had problems with bulbs that look and test good but the filament is actually disconnected on one side and is just touching the support. It works great until it doesn't and you never know when that will be. You might try swapping the bulbs left-right to see if the problem moves. OK, your first post says you changed the bulb. Scratch that idea.

If you haven't already, track down the ground (brown) wire for the headlamp and trace it to its terminal point on the body. Remove the screw and scrape/sand the terminal and body to bare metal. I had a lighting problem that was eventually traced to a bad ground. Again, not a good possibility since the high beam works but you never know.

Jeremy