Where can I find a wiring diagram for a 1989 20 hp Mariner?

You can find a wiring diagram for a 1989 20 hp Mariner outboard motor in the owner's manual or service manual for that model. Additionally, online resources such as boating forums, manufacturer websites, or dedicated outboard motor repair sites might offer downloadable diagrams. Websites like eBay or Amazon often sell manuals as well. Lastly, consider reaching out to a local marine mechanic or dealer for assistance.