Usually tjhey are a junction box from the passenger compartment to the engine compartment. They usually can be pried apart, but are fairly tight and most have ascrew or small bolt in the centre to keep them sealed and from coming apart. They also have a caulking to help seal around the firewall to prevent moisture coming in or corroding the connections. They also may have plastic tabs that lock them together.
Check around it and go slow so you do not do a lot of damage,You then may not be able reconnect properly.