Windshield wiper switch

I am wanting to change the switch in my car. I was hoping to save money and get the part off of another vehicle, I was wanting to know if it matter that the part would be from a 2003 Mercedes? Does the year matter? The signal works, dimmer etc, but the wipers themselves will not stay on when the switch is on. When you push it in they will still work manually, and will work when spraying but it won't stay on by themselves.