It's most likely the headlamp relay or a melted connection at the relay. I think your relay is located the same place as my `93...below the center dash vents, mounted in an awkward position behind the console. I located/accessed mine by removing the center console covers and shining a flashlight looking UP at the center vents. In my case, the melted white plastic connector housing gave it away...you're likely to find the same. Unfortunately, an all too common problem in late-model 240s. You might be able to simply clean up the connector pins, but a new housing & relay would be a more permanent fix.

Good Luck!