Turn Signal Switch
 

This is for a 1983 240D... a 123 body style.

I replaced the turn signal switch assembly and I am still having the same problems. The right side works great. But when I put on the left side it either turns off at the slightest move of the steering wheel or stays on after the turn and the steering wheel returns to the straight position until you make an over steer to turn it off.

Can anyone offer any guidance here???

You need to go into the section below the steering wheel and see where the plastic tabs are. It is possible that the car is improperly aligned and the steering wheel has been moved to compensate.