1985 w126 300sd headlamp won't turn off
 

This is very frustrating and not the first time it has happened.
Day or night, the headlamps and signal lights will come on by themselves and won't turn off without unplugging them at the connection harness.
I have replaced the headlamp switch twice in the past with used switches and then most recently with a new one, and while that worked for about 6 months, now it too doesn't help.
I have looked around at other sites to see if there is either a relay involved or ANY other solution, but I have found nothing to help.
HELP!

Maybe the bulbs you are using draw too much current and the switch contacts are getting fused?

X2 dieselbenz1

Have any upgrades such as bulbs, euro headlamps or fog lamps added?

Does any of the wiring that you can see or touch look burned or is no longer flexible causing high resistance/heat?

Do euro headlamps do this often? I ask because I have a pair for my 85 w126 body which came standard American.