Principles of Operation
WARNING: This page is about a different car, the 2013 Ford F-550 Super Duty, 2013 Ford F-450 Super Duty, 2013 Ford F-350 Super Duty, and 2013 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition is in the RUN or ACC state, the upfitter switch assembly receives voltage from the Body Control Module (BCM) fuse 44 (10A). The upfitter switches control the 4 upfitter relays in the upfitter relay box. When the relay is energized, voltage is supplied to the customer installed accessories.