Where can you find a diagram of the fuse blocks on your 1998 E350 Ford van?

Answer

In the owners guide. If you don't have one you can often go the library and look in their reference section. Most libraries have repair manuals there.

There is a diagram in the owners manual (page 125 for fuses, page 129 for relays).

Check out

http://vehicleownersmanuals.blogspot.com/

to download it for free.