F 150 4WD V8-4.6L VIN 8 (2010)
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Ignition OFF.
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Measure the voltage between the trailer battery charge relay pin 3, circuit SSB21 (GY/RD), BJB face side and ground.
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Is the voltage greater than 10 volts?
Yes
GO to AD6.
No
VERIFY the BJB fuse 21 (30A) is OK. If OK, REPAIR circuit SSB21 (GY/RD) for an open. TEST the system for normal operation. If not OK, REFER
to the Wiring Diagrams to identify the possible causes of the circuit short. See: Diagrams/Electrical Diagrams/Diagrams By Number
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AD6 CHECK FOR VOLTAGE TO THE TRAILER TOW BATTERY CHARGE RELAY USING THE RELAY GROUND PIN
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Measure the voltage between the trailer battery charge relay pin 3, circuit SSB21 (GY/RD), BJB face side and the trailer battery charge relay pin
2, circuit GD123 (BK/GY), BJB face side.