Backseat floorboard on Drivers side soaked and car is overheating on a 2001 Ford mustang, what could be the issue?

If a fuse blows then there is a short in the wiring or in whatever that fuse powers up, so there is no clear answer to what is the source of the short, you will need to determine the wire colors and what the fuse powers and check the whole circuit until the short is isolated. Even professional tech's hate this kind of a repair. Very time consuming in many cases, then once in awhile you get lucky. I did electrical diagnosis and repair my whole career, to me it is fun, not so much to others. If a fuse blows then there is a short in the wiring or in whatever that fuse powers up, so there is no clear answer to what is the source of the short, you will need to determine the wire colors and what the fuse powers and check the whole circuit until the short is isolated. Even professional tech's hate this kind of a repair. Very time consuming in many cases, then once in awhile you get lucky. I did electrical diagnosis and repair my whole career, to me it is fun, not so much to others.