A reliable repository that aggregates factory manuals. Their W639 edition is usually split into three PDFs (Engine, Body, Electrical). Ensure you select the year (pre-facelift 2003-2007 vs facelift 2007-2014) as the electrical architecture changed.
Searching for "Mercedes Vito W639 Workshop Manual PDF" on Google yields a minefield. Here is what you need to watch out for: Mercedes Vito W639 Workshop Manual Pdf - Google
Several platforms offer access to these manuals, ranging from official manufacturer sites to community-driven databases: A reliable repository that aggregates factory manuals