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Re-Wiring Old Travel Trailer to Convert from 5-Pole Flat to 7-Way RV Style Blade Connector


Hi there, I have an old travel trailer which I am rewiring and I have a question. The trailer has a 5-flat wiring harness on it, which is what I need, but I need a longer lead/plug to connect to the towing vehicle. The towing vehicle has a 7-blade plug. I am wondering if it would cause any issues to wire a 7-Way Molded Trailer Wire Connector 8foot Long code H20046 to my five flat wiring harness using a junction box by essentially omitting the unneeded wires on the 7-blade connector? As long as the wires are connected to the correct corresponding wires, can I expect any dysfunctions by doing this? Thank you!


Helpful Expert Reply:

When a tow vehicle and trailer have different style connectors the options are to re-wire one of them or to use an adapter. Adapters are fine for a quick fix but for long-term reliability you are better off doing exactly as you suggest - wiring in a new connector on the trailer to match the tow vehicle. This avoids the adapter and the potential for trouble down the road from the extra connection points.

A junction box like # 38656 is a perfect way to connect the 7-way harness # H20046 from Hopkins to your trailer's existing wiring. The linked video illustrates.

You will also need ring terminals to make the connections inside the box; you will need enough for all of the wires on both sides of the box. I suggest 3M ring terminals # 44-5310A which work with 10- to 12-gauge wires. You'll need a crimping tool to affix the ring terminals to your wire leads. You may prefer to order a re-wiring kit, part # HM51020 from Hopkins, since it includes the crimping tool and various other wiring components in a handy case. Note you'll still need to order some additional ring terminals as the kit includes only 2.

Take care to match the wires in the junction box by FUNCTION not by color. Trailers often use specific colors for specific functions but there is no guarantee that your trailer is wired in the conventional manner. So it is BEST to TEST. You can apply 12V power directly to each circuit on the trailer connector to confirm what that wire does. Once you know that you can match the wires up by function to those on the Hopkins molded connector # H20046.

There is a legend on the product page that tells you what each wire in the Hopkins connector does so you will know how to match your functions for both halves of the wiring joined in the box.

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