Ok example the ferrari 2002 steering wheel out the link you send.
The package contains 4 files
they have to be installed in the cars.wad folder
You open the cars.wad folder with easywad, that is installed when zaz tools is installed.
You open the wad and you get 3 folders.
In the folder Cars you put the file stwheel.Tex
In the folder Cars you have a subfolder called cockpit, there you put the other 3 files.
You close the wad and the steering wheel is installed !!!
This is an installation when you don't use a CSM mod !!!!