Rich, after your first comment in post #2 above I went and rechecked it. I noticed there were two different links to the catalog depending on the serial number of the coach. In one link, the electrical portion gave the 404 error but the other link worked fine (although it linked me to a Sunstar not a Vista). It's a fantastic tool, so even with a few little quirks I am glad Winnebago provides it.
2021 Winnebago Vista 35U towing a 2010 Cadillac SRX
2003 Itasca Sunova 30B