There is no wiring. The Field Unit runs on its own sealed 28 Wh lithium cell, which is what lets it go on breakers, buckets and other attachments that have no electrical supply of their own.
That also means there is no fuse to check and no harness to route. Battery life is quoted in transmissions rather than years (roughly 4,000 at one transmission per day), so reporting frequency, signal strength and temperature all affect how long a unit lasts in the field.