Is this a light switch problem?

Looking for some advice on a lighting issue for a '95 D110. (Yes, I know electrical issues are part/parcel of LRs!).

My left front running light AND my left rear night light are not working. (By night light I mean the top left bulb that has two filaments, one filament is for the brakes and that works; the other filament comes on when the lights are turned on, and now it does not come on).

I've replaced bulbs and light fixtures and it appears that this might be a light switch issue? It worked until about two weeks ago. Don't believe a single fuse would account for this outage, or would it?

Advice eagerly sought.

thanks
Keith