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How to Determine Functions to Wire New 7-Way to Trailer


I just purchased a used AutoMate trailer and I need to replace the old 7 pin pigtail with an updated 7 blade pigtail. The colors on the wiring include black, white, green, brown, blue and 2 red wires one large gauge and one small gauge. The blue and white wires are also large gauge wires. The old pigtail is gone so Im not exactly sure how to wire up the new pigtail. Thanks for your help.


Expert Reply:

The only way to correctly wire a new 7-way plug and lead like the Hopkins # H20042 or 7-way plug like the Bargman # 54-77-003 is to determine the functions of the wires, and unfortunately there is no kind of universal color code to tell us what wires do what.

So you'll need to determine that by using a separate 12 volt battery and using that to test each of the wires on the trailer to find out what their functions are. You will ground the negative terminal and use the battery's positive post for the wires which will tell you their functions.

To make it really easy I recommend using the etrailer Trailer Wiring 7-Way Upgrade Kit # e99011 which comes with a 7-way connector, junction box, ring terminals, wire loom and a self-tapping ground screw. I have added a link to an install video using this kit which I recommend taking a look at.

I have added a link to a help article on trailer wiring for you to check out as well as a link to our selection of trailer-side 7-way plugs.

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expert reply by:
Kyle S

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