The fuse and the relay are for the constant charge circuit in your 7-pin trailer power connector. Even if you don't use the trailer brake controller, you might want to install these if you will be pulling a trailer with break-away brakes that need to keep the battery charged, or with internal lights that you want to operate.
[SIGPIC]- 2010 F-150 Lariat SCREW 4x2 dark blue pearl
- 5.4l, 6 speed, 3.73 LS, 6.5 ft bed
- max trailer tow, nav, rear camera
- billet antenna, Bull Ring tie downs, 4WD conversion