Trailer Connections
Heavy-Duty Trailer Wiring Package
Your vehicle may be equipped with an eight-wire trailer
towing harness. This harness, with a seven-pin
universal heavy-duty trailer connector, is attached to a
bracket on the platform hitch.
The Center High-Mounted Stoplamp (CHMSL) wire is
tied next to the trailer wiring harness for use with a
trailer.
The eight-wire harness contains the following trailer
circuits:
•Yellow: Left Stop/Turn Signal
•Dark Green: Right Stop/Turn Signal
•Brown: Taillamps
•White: Ground
•Light Green: Back-up Lamps
•Light Blue: CHMSL
•Red: Battery Feed
•Dark Blue: Trailer Brake
Trailer Connections
(C7/C8 Models Only)
If your vehicle has these trailer connections, they are
located at the rear of the cab for a tractor and at the rear
of the chassis when towing a trailer. There will be an
air connection and an electrical connection.
Be sure that the couplings to the trailer are made
correctly.
Air Connections
If you are not connecting the trailer air line connections
to another piece of equipment, be sure to replace
their protective caps.
Electrical Connections
This system is a seven-wire cable that will connect to
the trailer, supplying power to the trailer’s lighting
system. When not in use, it is stored in the trailer
air-hose storage bracket.
4-26
4. With the coolant surge tank pressure cap off, start
the engine and let it run until you can feel the upper
radiator hose getting hot. Watch out for the engine
cooling fan.
By this time, the coolant level inside the coolant
surge tank may be lower. If the level is lower, add
more of the proper mixture to the coolant surge tank
until the level reaches slightly above the FULL
COLD mark.
5. Then replace the pressure cap. Be sure the
pressure cap is hand-tight and fully seated.
Engine Fan Noise
Your vehicle has a clutched engine cooling fan. When
the clutch is engaged, the fan spins faster to provide
more air to cool the engine. In most everyday driving
conditions, the clutch is not fully engaged. This improves
fuel economy and reduces fan noise. Under heavy
vehicle loading, trailer towing and/or high outside
temperatures, the fan speed increases when the clutch
engages. So you may hear an increase in fan noise. This
is normal and should not be mistaken as the transmission
slipping or making extra shifts. It is merely the cooling
system functioning properly. The fan will slow down when
additional cooling is not required and the clutch
disengages.
You may also hear this fan noise when you start the
engine. It will go away as the fan clutch disengages.
Power Steering Fluid
SeeScheduled Maintenance on page 6-5to determine
when to check your power steering fluid.
5-54
Fuse Usage
13Trailer Turn Signals/Hazard Warning
Flashers
14 Radio/Chime
15 Daytime Running Lamps
16 Airbag System
17 Exterior/Interior Lamps
18 Parking Brake
19 Accessory Power
20 Ignition 4
21 Sidemarker Lamps
22 Turn Signal/Backup Lamps
23 Transmission
24 Hydraulics/Air Brake
A Spare
B SpareFuse Usage
Blank Not Used
BRK Brake Warning Lamp
RT PRK Passenger Side Parking Lamps
Blank Not Used
Blank Not Used
LT PARK Driver Side Parking Lamps
RT REAR
TRN/STOPPassenger Side Rear Turn
Signal/Stoplamp
LT REAR
TRN/STOPDriver Side Rear Turn
Signal/Stoplamp
RADIO Radio
Blank Not Used
Blank Not Used
PWR WNDW Power Windows
5-105
Relay Usage
ECU/PTO*Engine Control Unit/Power Take-Off
*Diesel 7.8 DURAMAX
®
BRK LAMPC4/C5 Brake Lamps,
C6/C7/C8 Tractor/Trailer Wiring
DRL Daytime Running Lamps
IGN-4 Ignition
CHMSL Center High Mounted Stoplamp
MRK LTS Sidemarker and Clearance Lamps
HTD/MIRR Heated Mirrors
HTR Diesel Heated Fuel
RT TRN TRLR Passenger Side Trailer Turn Signal
Blank Not Used
LT TRN TRLR Driver Side Trailer Turn Signal
Blank Not Used
Blank Not Used
Blank Not Used
Underhood Fuse Block
When a circuit goes out, the problem could be in either
the primary or secondary underhood fuse blocks.
These blocks use blade-type fuses.
Both underhood fuse blocks are located in the engine
compartment, on the passenger side of the vehicle.To access the fuse blocks, gently squeeze both sides of
the cover to unlatch the tabs at the top. Then, unsnap
both attachments at the bottom and remove the cover.
Notice:Spilling liquid on any electrical components
on your vehicle may damage it. Always keep the
covers on any electrical component.
Be sure to replace fuses with fuses of the same rating.
Do not use fuses of higher amperage than those
indicated on the fuse block.
Primary Underhood Fuse Block
5-106
❑Rear axle service — Eaton®, Rockwell®, Spicer®
axles (or every 12 months, whichever occurs
first).(30)
❑Exhaust brake service, if equipped. Check for
excessive spindle free play and smooth operation.
Lubricate ball joint cap.
❑Inspect air compressor discharge port (or every
6 months or every 1,800 hours, whichever occurs
first).
❑Manual transmission (ZF 6-speed only) fluid
replacement (or every 48 months, whichever
occurs first).
❑Trailer brake hand control valve service (or every
12 months, or every 3,600 hours, whichever
occurs first).(35)
120,000 Miles (192 000 km)
❑C600, C700, and C800 Gasoline Engines Only:
Replace engine drive belts.
❑C400 and C500 Gasoline Engines Only: Engine drive
belts service (or every 12 months, whichever occurs
first).(17)
❑DURAMAX
®Diesel Only: Diesel Particulate Filter
(DPF) service. Then every 100,000 miles
(160 000 km).(7) (38)
150,000 Miles (240 000 km)
❑Cooling system service (or every 60 months since
last service, whichever occurs first).(2) (29)
❑Diesel Engine Only: Inspect engine drive belt;
replace as necessary.
❑Isuzu Diesel Only: Diesel Particulate Filter (DPF)
service (or every 4,500 hours, whichever occurs
first). Then every 150,000 miles (240 000 km),
or every 4,500 hours, whichever occurs first.(7)
200,000 Miles (320 000 km)
❑Rear axle service — Eaton®, Rockwell®, Spicer®
axles (or every 12 months, whichever occurs
first).(30)
❑Remove, disassemble, clean, and inspect the air
brake trailer supply valve (or every 2 years, or
every 7,200 hours, whichever occurs first).
❑Diesel Engine Only: Inspect engine drive belt;
replace as necessary.
250,000 Miles (400 000 km)
❑Four-wheel drive only: Front axle service.(30)
❑Four-wheel drive only: Transfer case service.(30)
❑Manual transmission (except ZF 6-speed) fluid
replacement (or every 60 months, whichever
occurs first).
6-19
(33)= Clean and lubricate air brake automatic slack
adjuster. Check pushrod travel and auto adjustment
operation. Have serviced if needed.
(34)= Air brake chamber service: Check operation,
mounting clamps, and air lines and check for leaks.
(35)= Trailer brake hand control valve service: Check
operation; lubricate cam and follower.
(36)= Tighten the wheel stud nuts to the specified
torque values at 100 miles (160 km). Thereafter, tighten
them 1,000 miles (1 600 km) after each time the wheel
is removed. SeeTightening the Wheel Nuts on
page 5-86.
(37)= Inspect and clean any accumulated dirt, gravel,
or other foreign objects from the valves and valve boots
as needed. Using light oil, lubricate brake pedal to
brake application valve linkage components. Check any
rubber boots for cracks, holes, or deterioration and
replace if necessary.(38)= Estimated minimum. Actual mileage depends on
fuel and oil consumed.
(39)= If the vehicle has the Isuzu diesel engine and is
used primarily for long trip, highway service, change
the engine oil and filter every 18,000 miles (28 800 km),
or every 12 months, or every 750 hours of engine
operation, whichever occurs first.
(40)= Make sure any safety belt reminder light and
safety belt assemblies are working properly. Look
for any other loose or damaged safety belt system parts.
If you see anything that might keep a safety belt
system from doing its job, have it repaired. Have any
torn or frayed safety belts replaced.
6-25
A
Accessories and Modifications............................ 5-4
Adding a Snow Plow or Similar Equipment.........4-23
Adding Equipment to Your Airbag-Equipped
Vehicle.......................................................1-59
Additives, Fuel................................................. 5-8
Add-On Electrical Equipment...........................5-102
Air Cleaner/Filter, Engine.................................5-39
Air Conditioning..............................................3-20
Air Pressure Gage..........................................3-46
Air Suspension...............................................2-44
Air Suspension Seats........................................ 1-6
Airbag
Off Light.....................................................3-29
Readiness Light..........................................3-28
Airbag System................................................1-48
What Will You See After an Airbag Inflates?....1-54
When Should an Airbag Inflate?....................1-52
Where Are the Airbags?...............................1-51
Airbag Systems
Adding Equipment to Your Airbag-Equipped
Vehicle...................................................1-59
Airbag Off Switch........................................1-56
How Does an Airbag Restrain?......................1-54
Servicing Your Airbag-Equipped Vehicle..........1-59
What Makes an Airbag Inflate?......................1-53
Antenna, Fixed Mast.......................................3-58Antilock Brake System (ABS)............................. 4-5
Antilock Brake, System Warning Light................3-34
Antilock Brakes, Trailer System Warning Light.....3-34
Appearance Care
Aluminum or Chrome-Plated Wheels..............5-98
Care of Safety Belts....................................5-96
Chemical Paint Spotting..............................5-100
Cleaning Exterior Lamps/Lenses....................5-97
Fabric/Carpet..............................................5-95
Finish Care.................................................5-97
Finish Damage............................................5-99
Instrument Panel, Vinyl, and Other Plastic
Surfaces.................................................5-96
Interior Cleaning..........................................5-94
Sheet Metal Damage...................................5-99
Tires..........................................................5-99
Underbody Maintenance.............................5-100
Vehicle Care/Appearance Materials...............5-100
Washing Your Vehicle...................................5-97
Weatherstrips..............................................5-96
Windshield and Wiper Blades........................5-98
Ashtray.........................................................3-20
Audio System.................................................3-47
Chime Level Adjustment...............................3-58
Fixed Mast Antenna.....................................3-58
Radio Reception..........................................3-58
Setting the Clock.........................................3-48
Theft-Deterrent Feature................................3-57
1
Audio System(s).............................................3-48
Automatic Transmission
Fluid..........................................................5-43
Operation...................................................2-29
B
Battery..........................................................5-66
Bench Seat, Split............................................. 1-6
Brake
Diesel Engine Exhaust.................................2-26
Emergencies................................................ 4-5
Exhaust Indicator Light.................................3-40
Trailer Hand Control Valve.............................. 4-6
Brakes..........................................................5-57
Hydraulic Systems......................................... 4-4
Parking Brake Burnish Procedure...................2-43
System Warning Light..................................3-32
Braking........................................................... 4-4
Braking in Emergencies..................................... 4-5
Break-In, New Vehicle.....................................2-10
Bucket Seats................................................... 1-2
Bulb Replacement...........................................5-76
Buying New Tires...........................................5-85
C
California Perchlorate Materials Requirements....... 5-5
California Proposition 65 Warning....................... 5-5Capacities and Specifications..........................5-109
Carbon Monoxide...................................2-45, 4-16
Care of
Safety Belts................................................5-96
Center Console Storage Area...........................2-53
Change Fuel Filter Warning Light......................3-44
Charging System Light....................................3-30
Check
Engine Light...............................................3-36
Gages Warning Light...................................3-42
Checking Things Under the Hood......................5-22
Chemical Paint Spotting.................................5-100
Child Restraints
Child Restraint Systems...............................1-35
Infants and Young Children...........................1-31
Lower Anchors and Tethers for Children..........1-40
Older Children.............................................1-28
Securing a Child Restraint in a Rear Outside
Seat Position...........................................1-40
Securing a Child Restraint in the Center Front
Seat Position...........................................1-44
Securing a Child Restraint in the Center Rear
Seat Position...........................................1-42
Securing a Child Restraint in the Right Front
Seat Position...........................................1-44
Where to Put the Restraint...........................1-38
Chime Level Adjustment..................................3-58
Cigarette Lighter.............................................3-20
2