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Complete Circuit
Proper Wire Gauge
Quality Electrical Connections
Solid Ground Wire
Correct Wiring Sequence
Power Source
Electrical Diagnostic Procedures
Short/Short to Ground
Brake Magnet Test
Brake System Amperage
Complete Circuit
Proper Wire Gauge
Trailer Wire Size
Number of
Brakes
Hitch-to-Axle
Distance in Feet
2
Trailer Wire Requirements
Recommended
Minimum Hookup
Wire Size (Copper)
12 AWG
4
Under 30
12 AWG
4
30-50
10 AWG
6
Under 30
10 AWG
6
30-50
8 AWG
Quality Electrical Connections
Preferred
Acceptable
Least Desirable
Solder Joint
(should be covered)
Insulated Crimp &
Heat Shrink
Connector
Insulated Piercing
Connector
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Need a ground wire across the hitch – don’t rely on just the
hitch for grounding
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Need a secure & dedicated wire from each brake – don’t rely
on the frame for grounding
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The frame is OK as an auxiliary or parallel ground path
Correct Wiring Sequence
Parallel Wiring
Series Wiring
Quality Electrical Connections
Preferred
Acceptable,
Not preferred
Inadequate
7-Way
Flat 5
Flat 4
Electrical Diagnostic Procedures
Components Required
12V Power Source
(battery or tow vehicle)
Multimeter
Terminology
voltage [vohl-tij] noun Electricity.
Voltage
electromotive force or potential difference
expressed in volts
amperage [am-per-ij] noun Electricity.
Amperage
the strength of an electric current measured in
amperes
ohm [ohm] noun
Ohm
Electrical resistance between two points of a
conductor; measured in ohms
Short/Short to Ground
Disconnect One Axle
Did that solve the problem?
Yes
No
Disconnect Other Axle
Did that solve the problem?
Disconnect One Brake
Did that solve the problem?
Yes
Yes
No
There is is an issue
with the trailer wiring.
Disconnect Other Brake
Did that solve the problem?
No
Problem is not
in the brakes.
No
Yes
There is an issue with the
brake magnet.
Electrical Diagnostic Procedures
Measuring Voltage
System voltage: measured at the magnets by
connecting the voltmeter to the two magnet lead
wires at any brake.
Voltage: should begin at 0 volts; as controller
bar is slowly actuated, should gradually increase
to about 12 volts.
Threshold voltage of a controller is the voltage applied to the brakes when the controller first turns
on. Lower threshold voltage will provide for smoother braking. If the threshold voltage is too high,
the brakes may feel grabby and harsh.
Electrical Diagnostic Procedures
Brake System Amperage
Measure amps at the BLUE wire of the controller, which is output to the brakes. The BLUE wire
must be disconnected and the multimeter put in series into the line.
The most common electrical problem is low or no voltage and amperage at the brakes. Common
causes of this condition are:
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Poor electrical connections
Open circuits
Insufficient wire size
Broken wires
Improperly functioning controllers or resistors
Another common electrical problem is shorted or partially
shorted circuits (indicated by abnormally high system
amperage). Possible causes are:
 Shorted magnet coils
 Defective controllers
 Bare wires contacting a grounded object
Electrical Diagnostic Procedures
Brake Magnet Test
Connect the multimeter between the positive terminal of a battery and one of the
magnet wires, then connect the other magnet wire to the negative battery terminal.
Check the amperage, if the amperage is greater than the specified amount, replace the
magnet. If the reading is less than the specified amount, then the leads are bad and the
magnet should be replaced.
Next disconnect the negative wire from the brake magnet wire and connect it to the
base, housing, of the brake magnet. If there is any
Brake
Amps/
Two
amperage the magnet is shorted and will need
Size
Magnet
Brakes
to be replaced.
Finally, using the multimeter check the resistance
between the brake magnet wires. If the resistance
is not within the specified range then the magnet
will need to be replaced.
Four
Brakes
Six
Brakes
Magnet
Ohms
7" x 1¼"
2.5
5.0
10.0
15.0
3.9
10" x 1½"
3.0
6.0
12.0
18.0
3.2
10" x 2¼"
3.0
6.0
12.0
18.0
3.2
12" x 2"
3.0
6.0
12.0
18.0
3.2
12¼" x 2½"
3.0
6.0
12.0
18.0
3.2
12¼" x 3 3/8"
3.0
6.0
12.0
18.0
3.2
 Non-Invasive
 Hubs/drums rotate freely
 Are the brakes adjusted?
 Invasive
 Remove the wheel and drum
 Inspect drum surfaces
 Inspect all brake parts
 Inspect magnet
 Inspect shoe and lining
Non-Invasive
Hubs/drums rotate freely
 What noises are heard? There is always a slight magnet noise.
 Any brake drag?
 Any tight spots?
 Are brakes adjusted?
Non-Invasive
How to properly adjust brakes
 Raise tire & wheel from ground
* Dexter custom brake spoon ideal for drop spindles and
areas with limited access
 Insert tool and engage adjuster star wheel
 Pry star wheel to rotate screw while rotating hub/drum
 Determine if tightening or loosening, then rotate star wheel and tighten adjuster until the drum
will not rotate by hand
 Then back off adjuster 6 to 8 notches until there is only a slight
drag on brakes
 Repeat for each brake
Invasive
Invasive
Removal/Inspection of the brake drum and surfaces
1.
Remove hub grease cap, cotter pin or retainer and spindle nut
2.
Remove outer bearing and washer
3.
Pull hub/drum from spindle
4.
Inspect drum surface:
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Drum bore should be smooth without grooves
Drum armature surface needs to be flat, small nicks
or grooves are OK
Wavy surface is NOT OK
Invasive
Inspect all brake parts
 Springs are not broken
 Lever arm moves freely and returns to original position
 Actuating block and lever are properly aligned
 Lever pivot bushing in working order
 Brake shoe webs are not bent
 Proper lubrication on all wear points and adjuster screw
Invasive
Inspect magnet
Magnet Face
 Wires are not broken
 Wire insulation is not damaged
 Magnet face is still flat
 Magnet face dimples still visible
Needs Replaced
Needs Replaced
New Magnet
Invasive
Inspect shoe and lining
 Shoe and lining are free from grease and oil
 Lining is at least 1/16” or more
 Lining is free from scores or gouges
 Hairline heat cracks are normal and are not
cause for concern
Acceptable Hairline Cracks