Here's where you should look:
* Your Owner's Manual: The most likely place to find it, although it might be simplified. Check thoroughly.
* Repair Manuals: A Haynes or Chilton repair manual specific to your 1986 Chevy Suburban 350 should have a detailed vacuum diagram. These are usually available at auto parts stores or online retailers.
* Online Forums: Websites and forums dedicated to classic Chevy trucks and Suburbans (e.g., forums on sites like Chevrolet Forum, etc.) are a great resource. Search the forums for your specific year, model, and engine. Members often post diagrams or can point you to where to find one.
* Local Auto Parts Store: Many auto parts stores (like AutoZone, Advance Auto Parts, NAPA) have access to repair manuals and databases which might include the diagram. They might even be able to print it out for you.
* eBay or similar online marketplaces: You might find a scanned copy of the diagram from a repair manual being sold.
Important Note: When searching online, be very specific in your search terms. Include the year (1986), make (Chevy), model (Suburban 350), and the *specific engine code* (found on a sticker under the hood or on the engine itself). This will greatly improve your chances of finding the correct diagram.