E 450 V8-5.4L (2009)
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Is the voltage greater than 10 volts?
Yes
The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
No
VERIFY the BJB fuse 57 (20A) is OK. If OK;
For vehicles equipped with a class I trailer tow package, GO to U3.
For vehicles equipped with a class II trailer tow package, GO to U2.
If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short.
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U2 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR (7-PIN)
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Disconnect: Trailer Tow C4099.
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Measure the voltage between the trailer tow C4099-6, circuit CAT17 (BN), harness side and ground.
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Is the voltage greater than 10 volts?
Yes
INSTALL a new trailer tow connector. TEST the system for normal operation.
No
GO to U3.
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U3 CHECK THE TRAILER TOW PARKING LAMP RELAY
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Place the headlamp switch in the OFF position.
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Disconnect: Trailer Tow Parking Lamp Relay .
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Substitute a known good relay.
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Place the headlamp switch in the PARKING LAMPS ON position.
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For vehicles equipped with a class I trailer tow package, measure the voltage between the trailer tow C4098-3, circuit CAT17 (BN), harness side
and ground.
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For vehicles equipped with a class II trailer tow package, measure the voltage between the trailer tow C4099-6, circuit CAT17 (BN), harness side
and ground.