Don't know if my H200 1998 is anywhere close to yours but here is a few shots of my fuel tank when I redid the floor
IMG_1779.JPG by
Jon Miller, on Flickr
assume yours is in the same place, it may have been carpeted over without being seemed which would require finding the edge and cutting....or worse yet the floor was replaced without leaving tank access.
I think with that link you can look at the rest of my photo stream to give a few more photos.
I also don't know the merc fuel system, but I just went through a fuel delivery issue with my Volvo and it involved replacing the pump (easy) and troubleshooting the electrical side of things (it gets power while cranking and running from two different sources via a relay and some diodes.....finally dug up the info with many many google searches usually ending up at Iboats.
good luck...welcome to the forum...lots of knowledgeable folks here but it doesn't get a whole lot of traffic, there is a fW facebook group that gets a lot of traffic but not so much expert help (imo)
_________________
Jon Miller
1998 four Winns Horizon H200
Volvo Penta 4.3 GL
Newtown, CT
untitled-545 by
millerjont, on Flickr