Well, I’m stumped!
I can’t easily pull my little trapdoor off, so I’ve left it alone, just in case a create a problem! I’ve been right through the Fiat handbook and there is no mention of it, nothing in the various diagrams and no description.
My only suggestion is to unscrew the foot panel in the footwell above it (inside the cab, about 6 or so screws) and see if anything is revealed there, underneath?
I’m intrigued. Keep us posted as to how you get on with this, Johnny.
Good luck!
Barry