Like many on here, my Prius has suffered problems in the wiring due to leaks into the battery compartment and tyre well. Taking apart the connectors, finds that the contacts have turned green and often corroded away. A simple enough fix, but on stripping back the wires, I found that several of the small diameter wires had turned black. Apparently this is due to oxidizing of the copper due to the dampness and can continue along the wires for several inches. Not sure of the long term effect, but I cleaned the ends of the wires the best I could and soldered them together. On researching the problem, I found that if they are dipped in vinegar overnight, they then turn back to bright copper and make a better soldered joint. Too late for my soldering, but I thought to pass on the tip for anyone else undertaking the task.
If you park your vehicle under/in covered storage, consider removing the drain plug beneath your spare tire, to allow water to drain out of that area in the even you experience water intrusion as so many have thus contributing to more corrosion.
I would not remove the plugs I would drill a drain weep hole in the plug itself Under the spare tire and in the bottom of the battery well. If missing plugs mice can easily get inside the car and wreck havoc on the wiring. Pretty common. Be careful with water in the battery well all the time it will rust out the bottom of that battery well and then no place to put the battery.