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Adding a 12 Volt Power Circuit to a 7-Way Trailer Connector on a 2010 Ford F-250  

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Ford F 250 superduty 5.4 L gas 2010 lariat pulling a Haulmark 6 by 12 tandem axle. Have 12 volt battery for power need a power cord from battery to round 7 pin on trailer

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Expert Reply:

On a trailer side 7-Way connector there should be a pin for 12-volt power. It is the pin that is in the 11:00 position if looking at the face of the 7-Way (1:00 position if looking at the back of the connector). You would run a wire from that location to the positive battery terminal to provide a maintenance charge to the trailer battery. If you need wire to go from the connector to the battery you can use # 10-1-1 which is sold in 1-foot increments.

If your 2010 Ford F-250 came with a factory installed 7-Way, then the 12-volt circuit should already be wired to the connector. Use a circuit tester like # PTW2993 to test the pin in the 1:00 position (front of connector) to determine if it is providing power. It should show power if it is connected. If it is not showing any power, then there could be a fuse or relay that needs to be replaced. Check the truck owner's manual to find the fuse/relays locations to check them.

If it does not work and the fuses and relays are good, you will need to get about 20 feet of wire # 10-1-1. At the back of the 7-Way in the 11:00 position, remove the existing wire if present and attach one end of the 10-1-1 wire. Then route the wire under the truck, avoid areas that can pinch or burn the wire, up into the engine compartment near the battery.

Under the hood you will need to secure a 40-amp circuit breaker, # PK54540, to the metal of the engine compartment. Attach one end of the wire to the AUX post of the circuit breaker. Save any extra wire and attach one end of it to the BAT post. Then attach the other end to the positive battery terminal.

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