CanBus addressing standards

[steve-V8s]

I am trying to get an understanding of how CanBus is implemented. I understand how the bus itself works, that is the easy bit, what I am trying to figure out is if there is any sort of standard for communication between applicable parts. If for example a Merc C class wants to switch the rear lights on does it talk to the same address as a Ford focus. Lots of cars have buttons on the steering wheel to do stuff, do these have common addresses or are they proprietary.

I am looking initially at cars but ultimately would like to understand the systems used in Agricultural machines. They all seem to declare ISOBUS capability which as far as I can see is Can Bus but are there any addressing standards.