Quick (however may not be permanent) fix:

Car: '87 300D Turbo
Problem: Headlight washer pump stuck on, constantly spraying fluid on the headlights anytime the switch for the lights is in anything but the "OFF" position.
Solution: Manually re-align the headlight wipers to be sure they are not stuck below the headlight or being prevented from wiping back and forth.

I tried this just now, and the fluid pump motor finally turned off when the lights were activated.

Hope that helps you out.