FORD 2008 F-550 v.3 - Manual (Page 299)

Always disconnect the battery before servicing high current
fuses.
To reduce risk of electrical shock, always replace the cover to
the Power Distribution Box before reconnecting the battery or
refilling fluid reservoirs.
If the battery has been disconnected and reconnected, refer to the
Battery section of the Maintenance and Specifications chapter.
The high-current fuses are coded as follows:
Fuse/Relay
Location
Fuse Amp
Rating
Power Distribution Box
Description
1 Relay Blower motor/Variable blower
control (Dual Zone Climate
Control)
2 Relay Electronic Shift-on-the-Fly
(ESOF) Lo-Hi
3 Relay Heater mirror
4 — Not used
5 30A* Trailer Brake Controller (TBC)
6 40A* ABS module (Pump)
7 30A* Upfitter auxiliary switch #1
8 30A* Upfitter auxiliary switch #2
2008 F-250/350/450/550 (f23)
Owners Guide (post-2002-fmt)
USA (fus)
Roadside Emergencies
299