Ford F-650 2018 Owner's Manual page 133

Brakes
System Park
E210344
With both knobs (A and B) pushed in
(normal driving position), the parking
brakes for both the tractor and trailer can
be applied by pulling the parking brake
knob (B) out, exhausting air from the
tractor spring brakes, simultaneously
causing the trailer air supply valve to pop
out, applying the trailer brakes.
Trailer Charge
E210342
If both knobs (A and B) are out, and you
want to recharge the trailer while leaving
the tractor spring brakes applied, the trailer
air supply (A) can be pushed in to recharge
the trailer air supply line. You can also use
this mode to park a combination vehicle
with tractor spring brakes.
130
F650750 (TBC) , enUSA, Edition date: 201708, First Printing