Is the software for the DOS wedge a file that just gets loaded randomly on the SD card as an isolated file, or does it have to be in some sort of folder or directory to work ?
The wedge is a tiny assembly program that installs itself at the top of BASIC memory. It puts a 'wedge' in the routine that looks at the commands entered from the keyboard. If it does not see a "@" or other special characters at the start, it simply lets the routine go on normally, but if it see the "@" character, it executes that shortcut command then returns to BASIC.
You should have the wedge program anywhere in the root directory of the SD card. You have to execute it only once with the load command LOAD"wedge",8 and run it. It will load itself into high BASIC and adjust the Top of BASIC pointer to protect itself. It is similar to a 'Terminate and Stay Resident' program in Microsoft DOS. The old wedge program has been around since day one at Commodore, but you should use the one referenced by the SD2PET page in case it has refinements needed to support subdirectories and image files although I imagine the code for that is in the SD2PET gadget. Do you have the full list of wedge shortcut commands? They are useful except for BASIC 4 users who have the 'Directory' and other commands which are just as good, well except for the subdirectory commands.