NAVEDTRA 14050a User manual

Trailer connections. Both the tractor and trailer have a seven-terminal trailer
receptacle that accepts the trailer electrical cable plug (Figure 6-54). Trailers used as a
part of double and triple trailers have trailer receptacles at both the front and rear of the
trailer to provide interconnection between trailers and dollies.
Figure 6-54 - Tractor-trailer connectors.
Because most tractors do not pull the same trailer all the time, the trailer receptacle and
cable are standardized throughout North America. The trailer interconnection is defined
by SAE recommended practice J560. Each of the seven circuits on all trucks and
trailers should be wired in the prescribed manner to permit tractors and trailers
throughout North America to be interchangeable.
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The color of wiring insulation for each trailer circuit is also standardized, as shown in
Figure 6-55. This wiring convention should be followed to aid in troubleshooting and
identification.
SAE J560 STANDARDS
Conductor
Identification Wire Color
Lamp and Signal Circuits
Wht White Ground return to towing vehicle
Blk Black Clearance, side marker & license plate
Yel Yellow Left-hand turn signal & hazard signal lamps
Red Red Stop lamps and antilock devices
Grn Green Right-hand turn signal & hazard signal lamps
Brn Brown Tail, clearance, side marker lamps, &
identification lamps
Blu Blue Auxiliary
Figure 6-55 - Trailer standard wiring colors.
Note in the schematic layout Figure 6-56 that the trailer running lights are broken down
into two circuits: the black wire and the brown wire. The black wire should be connected
to the front marker and clearance lamps, the identification lamp (three-bar light), the two
lower rear-side marker lamps, and the center marker lamps (if applicable). The brown
wire should be connected to the rear clearance lamps, the tail lamps, and the license
plate lamp. These circuits should be kept isolated from each other because they may be
protected by two different circuit protection devices in the tractor. Otherwise, a short
circuit at one place in the trailer running lamp wiring would disable all trailer running
lamps.
The illustration of the trailer plug and the trailer receptacle in Figure 6-57 is something
that you should become familiar with. It shows the views of the mating end of the tractor
receptacle and of the trailer plug. A test light or a special trailer light test tool is used to
test for voltage at the specific terminal to determine if the problem is with the truck or the
trailer. Notice the larger-diameter terminal at the top; this is the trailer ground terminal.
Because all trailer light current must pass through the ground circuit, it uses a larger-
diameter terminal than the other terminals and uses a larger-diameter wire than the
other wires in the seven-way cable.
The tractor normally provides the circuit protection for trailer wiring. However, some
trailers may have circuit breakers for trailer lights as well, (Figure-58). The trailer power
distribution module is usually mounted on the left frame rail aft of the cab or on a rear
crossmember at the end of the frame rail, as shown in Figure 6-59. The trailer PDM
contains fuses and relays to enable high current outputs via a wiring harness and relays
to enable high current outputs via a wiring harness to the trailer connector.
The length of the trailer wiring must be considered when replacing trailer wiring. Even
though the rear trailer lamps may have the same ratings as the truck lamps, the long
distance to the lamps can result in a substantial voltage drop on the wiring. This
reduces the voltage at the trailer lamps. Wire gauge is especially important for double
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and triple trailers because the total circuit from the rear trailer light feed to the tractor
can be more than 80 feet. Figure 6-60 should be used to determine the wire gauge
necessary for trailer wiring repair or replacement.
Conductor No. Color Key Lamp and Signal Circuits
1White Ground return to towing vehicle
2Black
x Side marker and identification lamps
3Yellow • Left-hand turn signal and hazard signal
4Red
Stop lamps and antilock devices
5 Green
• Right-hand turn signal and hazard
signal
6 Brown

Tail, combined rear clearance, and
license plate
7Blue
AUx Auxiliary, option lamps, dome, etc.
Figure 6-56 - Schematic layout of a trailer electrical system.
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Figure6-57 - Tractorandtrailermatingends.
Figure 6-58 - Trailer power distribution module.
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Figure6-59-TrailerPDMinstallation.
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TOTAL LENGTH OF CABLE IN CURCUIT FROM BATTERY TO MOST DISTANT
LAMP
12-Volt System
Amperes
(approx) Up to 30 Feet 40 Feet 50 Feet 60 Feet 80 Feet 100 Feet 120 Feet
Gauge Gauge Gauge Gauge Gauge Gauge Gauge
1.0 14
2 14
3 14
4 14
14 14
14 14
14 14
14 14
14 14 14 14
14 14 14 14
14 14 14 12
14 14 12 12
5 14
6 14
7 14
8 14
10 14
14 14
14 14
14 12
12 12
12 12
14 12 12 12
14 12 12 10
12 12 10 10
12 10 10 10
12 10 10 8
11 14
12 14
15 12
18 12
20 12
12 12
12 12
12 10
10 10
10 10
10 10 8 8
10 10 8 8
10 8 8 8
8 8 8 8
8 8 8 6
25 12 10 8 8 8 6 6
30 12 10 8 8 8 6 6
35 12 10 8 8 6 6 6
Recommended minimum wire gauge for stop light and ground circuits.
STOP LIGHT (Red) GROUND (White)
Single trailer (up to 50' length)
Doubles trailer (2-28' lengths)
Doubles trailer (2-40' lengths)
Triples trailer (3-28' lengths)
-12 Gauge
-12 Gauge
-10 Gauge
10 Gauge
10 Gauge
10 Gauge
8 gauge
8 gauge
Figure 6-60 - Recommended wire gauges for trailer wiring.
Figure 6-61 is a quick reference for troubleshooting electrical systems. It is always
recommended to refer to the service manual for detailed information for troubleshooting
and repairs.
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Electrical Troubleshooting
Description of Fault Possible cause
Stop lights on at all times Battery Mega Fuse that supplies the trailer
power distribution module (ODM) is open
or missing.
Trailer connector center pin (pin 7) is not
providing desired power condition Incorrect Reference Parameter
Intermittent or no electrical trailer operation
at all outputs Loss connection. Check trailer PDM
electrical connections and ground.
No operation on single output. Trailer PDM components are inoperable.
Check PDM fuse (blown) and relay (stuck)
for that output.
Intermittent or no operation on single
output Terminal connection(s) damaged wire.
Trace the suspect circuit.
Figure 6- 61 - Quick reference electrical troubleshooting.
11.5.1 Horns
The horn system uses a coil-operated diaphragm to produce sound waves and an
audible sound. The horn system is simple; it consists of:
1.
Fuseorcircuitbreaker - electricalsafetydevicethatprotectshorncircuitfrom
shorts
2. Hornwiringharness - wiresthatconnectfusetoharnessand hornstohorn
button switch
3. Horns - diaphragm-operateddevicesthatvibratetoproducesoundwaves
4.
Hornswitch - steeringwheel-orsteeringcolumn-mountedswitchforcompleting
horncircuit
Figure 6-62 shows a basic horn system. Power is present at the horns and in the
harness whenever the ignition switch is turned on. The horns switch grounds the circuit
to activate the horns.
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Figure6-62 - Horncircuit.
When the driver presses the horn
button, the wire leading from the
horns is grounded. This causes
current to flow through the fuse
and horns. The resistance in the
horn coils limits how much current
flows into ground.
When the driver releases the horn
button, a spring pushes the
switch back open. This breaks or
disconnects the ground circuit. No
current can then flow through the
horns and they stop sounding.
Horn nomenclature. A cutaway
view of a typical horn is given in
Figure 6-63. It is made up of the
following components:
1. Horn coil - set of windings
thatproducemagneticfield
whenenergizedbycurrent
flow
Figure6-63 - Cutawayviewofahorn.
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2. Contacts - breakerpointsthatopenandclosetocontrolcurrentflowthrough
horncoil
3. Diaphragm - flexiblemembraneinhornthatmovesbackandforthtoproduceair
wavesandsound
4. Plunger - metalcorethatisattachedbymagneticfieldofcoilwindings
5. Wireterminal - connectorformakingelectricalconnectionwithwiringharness
6. Outlet - openingofhornhousingfordirectingsoundtofrontofvehicle
When the driver presses the horn button, current flow enters the wire terminal and horn
coil. A magnetic field forms around the coil. The field attracts and pulls the plunger into
the coil. Since the plunger is attached to the diaphragm, the diaphragm is flexed back
toward the coil.
With enough movement, the edge of the plunger touches one of the contact point arms.
This pushes the contacts open and interrupts the current flow through the coil. Without
current, the magnetic field collapses, and the diaphragm snaps or flexes back into its
normal position.
Once the diaphragm and plunger move back, the contacts reclose. This reenergizes the
coil and the diaphragm is again pulled back toward the coil. The process is repeated
rapidly and the diaphragm vibrates back and forth in the horn housing. The resulting
vibration set up in the surrounding air can be heard as a "honking" sound.
A tone adjustment screw is normally provided for changing the sound of the horn. It can
be turned to affect the action of the contact points and frequency of the diaphragm
vibration.
Horn relay. A horn relay is sometimes used between the horn switch and the horns. It
is used to reduce the amount of current flowing through the horn switch.
When the driver presses the horn switch, a small current flow enters the horn relay. This
energizes the small coil in the relay to close the relay contacts. Then, a larger current
flows through the closed relay points and to the horns.
Horn Service. When a horn will not sound, check the fuse and connections, and test
the voltage at the horn terminal. If a horn blows continuously, the horn switch may be
bad. A relay is another cause of horn problems. The contacts in the relay could be
burned, or they may be stuck together.
A horn current adjusting screw is sometimes provided on the horn to set the amp draw
through the horn. To adjust horn current, connect an ammeter between the feed wire
and horn terminal. To prevent meter damage, be sure the ammeter can read more than
30 amps.
Get another person to sound the horn while you read the meter. If the current is not
within specifications (typically 4-5 amps), turn the amps screw on the horn until the
meter reads properly. Also, make sure you are getting adequate supply current/voltage
and there is not a high resistance in the horn circuit. If you cannot get the horn to read
within current specifications, replace it or isolate the circuit problem.
11.6.0 Small Accessory Motors
11.6.1 Windshield Wipers
A typical windshield wiper system is made up of a switch, wiper motor assembly, wiper
linkage, wiper arms, and wiper blades. Either a fuse or circuit breaker protects the
system.
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The windshield wiper switch is a multiposition switch that sometimes contains a
rheostat. Each switch position provides a different wiping speed. The rheostat operates
the delay mode for slow wiping action. A relay is frequently used to complete the circuit
between the battery and the wiper motor.
A wiper motor assembly consists of a permanent magnet motor and a transmission. The
wiper motor transmission changes rotary motion into a back-and-forth wiping motion.
The transmission is normally a set of plastic gears, an end housing, and a crank.
On the windshield wiper assembly the drive crank on the transmission connects to the
wiper linkage.
The wiper linkage is a set of arms that transfers motion from the wiper motor
transmission to the wiper arms. The rubber wiper blades fit on the wiper arms.
Windshield wiper service. Windshield wiper blades should be inspected periodically. If
they are hardened, cut, or split, replace them.
With electrical problems in a wiper system, refer to the service manual and its wiring
diagram of the circuit. First, check the fuses and electrical connections. If they are good,
use a test light to check for power to the wiper motor.
If power is being fed to the wiper, the motor or transmission may be at fault. Before
replacing the motor or transmission gears, make sure the motor is properly grounded. If
power is not reaching the wiper motor, check the wiper switch and circuit connections
for openings.
If the windshield washer does not work, check the fuse and connections. Use a test light
to check for power going to the motor. If the test light does not glow, the wiper switch
may be bad.
When working on a windshield wiper system, always follow the exact recommendations
given by the manufacturer, as systems and procedures vary with each vehicle.
Normally, the wiper motor must be replaced as a unit. The transmission gears are
usually the only serviceable part in the assembly.
11.6.2 Windshield Washer
A windshield washer consists of a solvent reservoir, pump, rubber hoses, connections,
and washer nozzles. The solvent reservoir, located in the engine compartment, holds a
supply of water and solvent. When the washer switch or button is activated, the wiper
motor and washer pump turn on. Solvent is forced out of the reservoir and onto the
windshield.
There are two common types of pumps used with windshield washer systems: a rotary
pump and a bellows (diaphragm) pump. Most new vehicles use a rotary pump mounted
in the solvent reservoir. A tiny electric motor spins an impeller, which forces the washer
solution onto the windshield. A bellows pump is normally mounted on and powered by
the wiper motor.
Windshield washer service. Many washer problems are caused by restrictions in the
fluid lines or nozzles. To check for restrictions, remove the hose from the pump and
operate the system. If the pump ejects a stream of fluid, then the fault is in the delivery
system. The exact location of the restriction can be found by reconnecting the fluid line
to the pump and disconnecting the line at another location. If the fluid still streams out,
the problem is after that new disconnect. If the fluid does not flow out, the problem is
before the hose was disconnected. Repeat this process until the problem is found.
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