I say to check (or replace) both headlight relays that are located in the fuse & relay box that is next to the battery.
I [also] have a Ford Focus that I put a pair of European ST-170 headlamps onto back in 2002, and not more than a week later, the lowbeam relay failed and then eventually the highbeam relay failed shortly thereafter. I replaced both relays and have never had a problem since.
You can use the micro-relays from a Ford Focus, for example, because they are easily soured from an aftermarket parts store (e.g. NAPA; AutoZone; etc.) and this is a relatively inexpensive thing to do.
This is may not be a cure however because electrical gremlins can and do stay around and/or are somewhat difficult to trace down.