Small sprayers and fertilizer spreaders don’t pull much power. They could easily work off the SAE connectors (battery tender connection). It would be easy to put a switch in line and run it to the cab through the back window
I'd suggest replacing that with a standard SAE quick connector. A good example is the battery connector you get for a Battery Tender charger. Amazon has a zillion SAE quick connector options. Plus you can use it to keep your battery charged.