Curt Manufacturing DISCOVERY User manual

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For use with 12 volt negative ground systems only
For trailers with two to eight brakes
Read, follow and save this guide for future reference
DISCOVERY
DISCOVERY BRAKE CONTROL
INSTALLATION AND USER GUIDE
51120-INS-R1 •

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This package includes:
(1) Brake control module with quick plug
(1) Mounting bracket
(4) Mounting bracket screws
One or more of the following may be needed to complete installation:
•Brake control connection harness, supplied with the tow vehicle (if equipped)
•CURT quick plug - custom connector for specic vehicles. See catalog for availability
•CURT part# 51515 - male quick plug with pigtails
•CURT part# 51500 - brake control wiring kit
Key Features
•Display shows provides detailed brake force output
•Mount anywhere in your vehicle
(Dependable solid state electronics require no leveling)
•Electronic activation ensures smooth stops
•No internal moving parts
•Fully-adjustable power and time (sync)
•Provides automatic and manual trailer braking
•Manual control lever activates brake lights
•Compatible with electronic systems (anti-lock brakes and cruise control)
•Self diagnostic - continually monitors trailer connection and checks for short circuits

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Controls and Components
1. Display
2. Sync adjustment
3. Output adjustment thumb wheel
4. Manual control lever
5. Quick plug connector
3
2
4
1
5

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Output Control
The output control establishes the maximum
amount of power available to the trailer brakes.
As the output control is moved to the right, more power will be available
to the brakes when the brake pedal is pressed or the manual control is used.
The output control should be adjusted during initial setup, when trailer load
changes, when different trailers are used or to adjust for a change in road conditions.
The output setting is shown on the digital display when a trailer is connected and
the brake pedal is pressed or the when manual control lever is actuated. The output
setting is shown as 0 through 10, with 0 being the minimum and 10 the maximum.
Sync Control
The sync control is located on the right side of the brake control unit and is responsible
for adjusting trailer brake aggressiveness. The trailer brakes become more aggressive
as the switch is moved toward the rear of the tow vehicle.
To view the sync setting on the display, press the brake pedal (trailer must be connected)
and move the sync control slightly. The display will change to the sync mode.
The sync setting is shown as 1 through 9, with 1 being the least aggressive and 9 being
the most aggressive. The sync adjustment has no effect on the manual control. The sync
control should be adjusted for individual driver preference or changing road conditions.

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Manual Control
The manual control lever is located on the front left of the brake control unit.
It only applies to the trailer brakes. Manual control is used during initial setup and
in situations where a slow reduction in speed is desirable.
When the manual control is pushed to the right, the control begins to apply
the trailer brakes. The further to the right it is pushed the harder the brakes
are applied until the maximum set by the output control is reached.
The output setting will be shown on the display and can be adjusted when using the
manual control. The manual control activates the tow vehicle and trailer stoplights.
Digital Display
The digital display shows the output
setting when the control is activated.
It is used to setup and monitor the
brake control and can be used when
trouble shooting.
Control activated
No trailer connected
Brake pedal pushed
Sync control activated
Trailer connected
Short or overloaded brake circuit
See trouble shooting guide
Internal control error
See trouble shooting guide
Control activated
Trailer connected

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Mounting the Brake Control
NOTE: Avoid mounting the brake control module near a CB radio or other RF transmitter.
Vertical
Horizontal
Any angle

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1. Determine a suitable mounting location.
Mount the unit securely to a solid surface where it is easily accessible to the driver.
The area behind the mounting location must be clear to prevent damage while drilling.
2. Hold the mounting bracket in the position selected
and mark hole locations through the slots in the bracket.
3. Using a 1/8" diameter bit, drill holes in the marked locations.
4. With a philips screwdriver, secure the bracket in place using the two
screws provided. Be careful not to strip the holes by over-tightening.
5. Mount the brake control unit in the bracket using the two
screws provided, as shown in the illustration on page 6.
Wiring
NOTE: Removal of factory supplied quick plug may void warranty.
Most pick-ups and utility vehicles are equipped with a plug from
the factory that allows quick brake control installation. Check the
owner's manual for plug availability, location and installation.
If the mating plug supplied with the vehicle is no longer available, a CURT
quick plug can be used. See the CURT catalog for application information.
For tow vehicles not equipped with a factory brake control plug,
we suggest CURT brake control wiring kit, part# 51500.

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IMPORTANT: Make sure that both positive and ground connections are made directly to
the tow vehicle's battery. Connecting to existing wiring or chassis ground, other than the
battery terminal, may damage vehicle circuits and could lead to trailer brake failure.
Mount a 30 amp, auto reset, circuit breaker as close to the battery as possible.
WIRING DIAGRAM

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IMPORTANT: When passing wire through sheet metal, always go through an existing
grommet, add a grommet or use silicone sealer to protect the wire from sharp edges.
Feed two 10 gauge, or larger, wires, one white and one black, from the mounted brake
control to the battery area. Using a ring terminal, connect the black wire to the 'aux' side
of the 30 amp circuit breaker. Leave the white wire for connection later.
Using a 10/12 gauge butt connector, attach the black wire from the 'aux' side of the
30 amp circuit breaker to the brake control's black wire. Using a 10/12 gauge butt
connector, attach the white wire from the battery area to the brake control's white wire.
Run a 10 gauge blue wire from the tow vehicle's trailer plug 'brake' terminal to the brake
control. Using a 10/12 butt connector, connect this wire to the brake control's blue wire.
Connect the brake control's red wire to the cold side
of the tow vehicle's stoplight switch using a wire tap.
NOTE: When making the stoplight switch connection on Ford / Mercury vehicles, do not
connect to the red wire with green stripe. Connect to the light green wire only.
For 1989 - 1991 Ford E and F series vans and trucks with anti-lock brakes, nd the
crescent shaped connector located on the steering column. The connector has two
rows of wires, the wire needed is the light green wire, second from the end in the
outside row. See the view shown in the wiring diagram on page 8.
For all other vehicles, use a test probe to nd the cold side of the stoplight switch. Probe
the switch wires until a wire is found that is only on when the brake pedal is pressed.

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IMPORTANT: Once a cold side wire is found, test to ensure that the wire is not grounded
when the pedal is in the up position. If the wire is grounded, the brake control unit will be
destroyed when manual control is used.
Reconnect the tow vehicle's negative battery terminal and attach the white, 10 gauge
wire previously positioned near the battery to the negative terminal using a ring terminal.
Using 10 gauge stranded wire and a ring terminal, connect the
'battery' side of the circuit breaker to the positive battery terminal.
Secure all loose wires with cable ties so that they will not be damaged and reconnect
the battery. See vehicle's owner's manual for special re-connection instructions.
To test installation, without a trailer connected, push the brake pedal. A single decimal
point ( . ) should light up on the display. If the decimal point does not light or if OL or Er is
shown on the screen go to the 'Troubleshooting' section.
Setup
Preliminary adjustments: With the trailer connected press and
hold the brake pedal, the display will show the output setting.
Adjust to 2.0 by turning the output control right or left as needed.
While still holding the brake pedal, move the sync control slightly. The display will change
to the sync setting. Adjust to 4o by sliding the sync control ahead or back as necessary.

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Test Drive
In an open area, such as a large parking lot, drive forward and apply the trailer brakes
using the manual control. If the trailer brakes are weak adjust the output control to the
right. If the trailer brakes jerk or lockup adjust the output control to the left.
Repeat this step until rm braking is felt without lockup.
Once the output is set, drive forward and press brake pedal. The tow vehicle and trailer
should both make smooth stops. If the stops seems slow and more aggressive braking is
desired, move the sync control toward the rear of the vehicle while holding the brake pedal.
If the stop seems too aggressive, adjust the sync control toward the front of the vehicle while
holding the brake pedal. After making a sync adjustment the display will show the setting
until the brake pedal is released. Make several stops at various speeds and adjust sync until
stops are smooth and rm. Slight adjustment the output control may also be desirable.
Helpful Tips
Light pressure on the brake pedal will activate the trailer's brakes with no effect on the
tow vehicle's brakes. This is useful for gradual slowing on steep grades or before stops.
Periodic adjustment of the sync and output controls may be necessary to correct for
changing road conditions, trailer loading, brake wear, and / or driver preference.
In some applications, when towing with hazard ashers on, the digital display will ash with
hazard ashers. If the brake control is set aggressively this may be felt in the trailer brakes.

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Bench Test Instructions
Wire as shown below.
Bench Test Wiring

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Set the output control to maximum and set the sync control to minimum.
NOTE: If at any time during the bench test the display shows OL, make sure that the blue
'brake' wire is not shorted to the 'negative' battery terminal or the white 'battery' wire.
If at any time during bench testing, the display shows Er,
return the unit to your CURT dealer for further evaluation.
Test Standby Condition
Hold the red 'stoplight' wire on the '+' battery terminal. The display should show
a single decimal point. This indicates correct wiring and that the control is ready.
Disconnect the red 'stoplight' wire from the battery.
Test Brake Pedal Activation
Ground the light bulb to the 'negative' terminal of the battery.
Re-attach the red 'stoplight' wire to the 'positive' battery terminal.
The display should step up to 10 and the bulb should start dim and slowly get brighter.
With the red wire still hooked up, slowly move the output control left. The display
should step down to 0 and the bulb should dim and go off.
Slowly move the output control back to the right. The display
should step up to 10 and the bulb should return to full brightness.

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Slowly move the sync control to the maximum. The display
should change to the sync mode and count up to 9o.
Disconnect and reconnect the red wire. The bulb should light brightly
with no delay, the display should read 10. Disconnect the red wire.
Test Manual Activation
With the output control still set at maximum, slowly activate the manual control slide button.
The bulb should start dim and get brighter and the display should
count up to 10 as the manual control is pushed.
While holding the manual control all the way in, slide the output control
up and down. As the output changes, the bulb should go bright and dim
and the display should read 0 to 10.
If the brake control unit does not function as described, return it for service or replacement.
NOTES

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Troubleshooting Guide (test without trailer first)
Condition Display Icon Probable Cause Probable Solution
No Trailer Connected
Decimal point does not light when
brake pedal or manual control is used
Blank No power to control, to ground,
reversed black and white wires,
circuit breaker blown
Check and repair connections.
Refer to the 'wiring' section
Decimal point does not light when brake
pedal is pushed. Does not light w/ manual
Pedal
Manual
No connection or incorrect
connection at stoplight switch,
blown fuse in stoplight circuit
Check and repair connections.
Refer to the 'wiring' section,
check stoplight circuit
Decimal on all the time Decimal
Only
Red wire connected to the wrong
side of the stoplight switch or to
wrong switch (cruise control)
Check and repair connections.
Refer to the 'wiring' section
Display shows output setting Output
Setting
Brake control unit
incorrectly wired
Check and repair connections.
Refer to the 'wiring' section
Display shows OL when activated Flashing
OL
Short in blue wire circuit Locate and correct short
Display shows Er Error Internal brake control problem Return unit to
dealer for evaluation
Trailer Connected
No trailer brakes, pedal or manual Decimal
Only
No connection between the
brake control and brakes
(blue wire circuit)
Confirm connection to trailer
connector, confirm connector
terminal positions, check trailer
No trailer brakes, pedal or manual Output
Setting
Trailer connector
incorrectly wired
Confirm trailer connector
terminal position
No trailer brakes, pedal or manual Flashing
OL
Short or overload
in trailer brakes
Troubleshoot trailer brake circuit per
brake manufacturer's instructions
No trailer brakes, pedal or manual Error Internal brake
control problem
Return unit to
dealer for evaluation
Weak or no trailer brakes Output
Setting
Trailer connector
incorrectly wired
Check and correct
connector positions
Trailer brakes on all the time Blank Trailer connector
incorrectly wired
Check and correct
connector positions