Lightning seeks a ground. When you have a weathervane on your roof, it is really only a piece of metal with no ground. As such, it is not susceptible to lightning strikes. Running a ground wire from a weathervane could actually harm the structure it is on, so you should refrain from grounding one.The exception to this is if you already have a lightning protection system on your barn or house. In this scenario, you’ll probably want to connect your weathervane to it.