Ford F-650 2001 Owner's Manual page 120

Driving
Actuation of trailer parking or emergency brakes
To actuate the trailer brakes only,
pull out the red control (trailer air
supply), exhausting the trailer
TO
supply line. The trailer brakes are
now applied either by air emergency
TRAILER
or spring brakes, depending on the
AIR SUPPLY
type of trailer system. This mode
NOT FOR PARKING
would be used to uncouple from the
trailer during bob-tail operation.
TO
System park
With both controls in for normal run modes, the parking brakes on both
tractor and trailer may be actuated by pulling the yellow control (parking
brake) out, which exhausts the air from the tractor spring brakes and
simultaneously causes the red control (trailer supply) to pop out,
applying the trailer brakes. This complies with federal regulations stating
one control must apply all the parking brakes on the vehicle.
Trailer charge
If both controls are out when parking the combination vehicle and it is
desired to recharge the trailer (leaving the tractor spring brakes
applied), the trailer air supply control may be pushed in, repressurizing
the trailer supply line. This mode could also be used to park a
combination vehicle with air actuated emergency brakes on the trailer to
provide demonstrated parking capability with tractor spring brakes only.
Automatic application
With both controls in (in the normal run configuration), if the supply
pressure to the push-pull valves is reduced to approximately 240 to 310 kPa
(35-45 psi), the red control (trailer supply valve) must pop out, applying the
emergency or parking brakes on the trailer. If the red control is held in
manually and the pressure decreases to approximately 172 to 240 kPa
(25-35 psi), a tripper piston within the MV-3 valve will move upward. This
will exhaust the trailer supply, causing the required non-override feature.
The yellow control (parking brake) will pop out at approximately 138 to
207 kPa (20-30 psi).
120