F 150 4WD V8-4.6L VIN 8 (2010)
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For the 7-pin connector, while applying the brake pedal, measure the voltage between the trailer tow C439a-1, circuit CAT06 (YE), harness side
and ground.
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Is the voltage greater than 10 volts?
Yes
REMOVE the known good relay. INSTALL a new trailer tow turn relay. TEST the system for normal operation.
No
REMOVE the known good relay. GO to Z5.
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Z5 CHECK FOR VOLTAGE TO THE LH STOP/TURN LAMP RELAY COIL
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While applying the brake pedal, measure the voltage between the trailer tow LH turn relay pin 1, circuit CLS18 (GY/BN), BJB face side and
ground.
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Is the voltage greater than 10 volts?
Yes
GO to Z6.
No
REPAIR circuit CLS18 (GY/BN) for an open. TEST the system for normal operation.
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Z6 CHECK THE VOLTAGE SUPPLY CIRCUIT TO THE LH STOP/TURN LAMP RELAY
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Measure the voltage between the trailer tow LH turn relay pin 3, circuit SBB45 (GY/RD), BJB face side and ground.
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Is the voltage greater than 10 volts?
Yes