E 450 V8-5.4L (2009)
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Ignition ON.
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Measure the voltage between the trailer tow 4-pin connector, harness side and ground as follows:
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Is any voltage present?
Yes
GO to W3.
No
The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
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W3 CHECK THE TRAILER TOW RELAY
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Ignition OFF.
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Disconnect: Suspect Trailer Tow Relay.
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Ignition ON.
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Measure the voltage between the trailer tow 4-pin connector, harness side and ground as follows:
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Is any voltage present?
Yes
REPAIR the circuit in question for a short to voltage. TEST the system for normal operation.
No
INSTALL a new trailer tow relay for the one in question. TEST the system for normal operation.
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W4 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR
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Ignition ON.
