How to Add Secondary 7-Way Round Connector to Semi Truck

Updated 03/17/2016 | Published 03/15/2016

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Question:

I work at an engineering firm and have been asked if a specific application can be done. The client has a semi with 7 way round socket that has an existing cable plugged into it. They would like to have an adapter that can be plugged into the existing socket to allow the existing 7 way cable to be plugged into that adapter but also have the adapter give them an additional 12v pigtail or additional socket built into the adapter for a separate device that needs to be under power during transport. This is proving very difficult to find. I there a multi adapter that gives a strait pass through of the 7 way round that also gives an additional 12v connection point at the adapter?

asked by: Jason V

Expert Reply:

Semi truck connectors are typically wired differently than those on pickups that are used for recreational towing. The linked article on wiring includes diagrams that show the various configurations in use. In certain circumstances wiring adapters can help but we offer no 1-to-2 type adapter like what you describe. Also functions can be assigned to different wires on a semi and so some adapters may not work.

If you need to have a second of the same type of 7-way connector available with only 12V auxiliary power (no lighting signals) then you could simply install an additional RV-style 7-way # 37185 and connect only the white ground wire to the frame and the black 12V power wire to the battery, using either a fuse or circuit breaker like # PK54540 to protect the vehicle. You'll want to use 10-gauge wire # 10-1-1.

expert reply by: Adam R