warning lights coming on when switching on headlights

[kildair]

Help please,
I have a 1999 E240 estate.
When switching the main headlights, varios warning lights come on including the ABS, BAS/ASR and handbrake on. In addition, the horn does not work.
Any advice. I remember in the past that on one occasion I had to change the brake light switch as the ABS light came on and had no cruise control.
Please advice
thanks

 

[kildair]

Folks, someone out there must have an answer. Pleeeeaaase help