Keyless Entry Rear Antenna
WARNING: This page is about a different car, the 2019 Ford F-550 Super Duty, 2019 Ford F-450 Super Duty, 2019 Ford F-350 Super Duty, and 2019 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
The keyless entry rear antenna is wired to the BCM. When activated, it transmits a low frequency signal to activate a passive key.