The Function of the Auxiliary 12-Volt Connection on the 7-Way Trailer Connection
Updated 09/11/2025 | Published 12/14/2016
Question:
What is the function of the 12 volt battery in this type of trailer? Can the interior light be turned on with the trailer NOT connected to the tow vehicle?
asked by: Russ F
Expert Reply:
The auxiliary 12-volt wire that runs from the 7-way connection to 7-way trailer plug will supply 12-volt power from the vehicle to the trailer. The 12 -volt power will allow interior or exterior lights to run that are not wired in to the trailer's tail and clearance lights. The light will operate separate from the trailer clearance and tail lights and will not need to have the truck light turned on to work. The auxiliary wire will also allow you to use other 12-volt trailer accessories, like an electric jack. This auxiliary 12-volt can also supply a maintenance charge to the trailer's battery and breakaway battery.
If you have a 4-way flat plug, then your interior trailer lights must work only when you have your tow vehicle's lights on and connected to the trailer.
Unless you have a separate 12-volt battery connected to your trailer, the interior trailer lights will not work if not connected to the tow vehicle.
Also, keep in mind that leaving the electrical connected between your vehicle and trailer over a period of time can cause your vehicle's battery to drain.
Sid 0.
4/9/2024
When is the Aux power supply hot ? Only when the ignition is on ? -OR- Hot all the time like a cigarette lighter socket ? Thanks Sid.
Product Page this Question was Asked From
Adapter 4-Pole to 7-Pole and 4-Pole
- Custom Fit Vehicle Wiring
- Wiring Adapters
- Universal Fit
- 4 Flat to 7 Blade
- Plug and Lead
- Hopkins
more information >
Continue Researching
- Shop: Trailer Hitch
- Article: Trailer Wiring Diagrams
- Search Results: trailer wiring
- Q&A: What is the AUX Power Pin for on a 7-Way Trailer Connector
- Shop: Trailer Wiring
- Search Results: gooseneck hitch
- Shop: Brake Controller
- Shop: Curt Trailer Hitch Receiver - Custom Fit - Class V Commercial Duty - 2-1/2"
- Article: Wiring Trailer Lights with a 7-Way Plug (It's Easier Than You Think)
- Shop: Vehicle Tow Bar Wiring
- Shop: TorkLift StableLoad Suspension Upgrade for Upper Overload Springs
- Search Results: distribution box
- Search Results: portable solar panel
- Q&A: Which Pin On A 7-Way Should Have Constant 12V Power When Vehicle Is Running
- Shop: Curt Trailer Hitch Receiver - Custom Fit - Class V Commercial Duty - 2-1/2"
- Shop: Curt Trailer Hitch Receiver - Custom Fit - Class V Commercial Duty - 2-1/2"
- Q&A: Does the TorkLift StableLoad # TLA7200 Require Drilling for Installation on My 2022 Ford F-250?
- Search Results: battery charge line
- Search Results: charge line kit
- Search Results: dexter drum 8 247
- Shop: Hopkins 7-Way RV Style Connector w/ Molded Cable and LED Test Lights - Trailer End - 8' Long
- Shop: Adapter 4-Pole to 7-Pole and 4-Pole
- Q&A: Can I Charge My Trailer Battery Using 7-Way Trailer Connector on Truck
- Article: 4 Steps to Choosing Your 5th Wheel Pin Box
- Article: Fifth Wheel Trailer Hitch Information and Installation Tips
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Article: Breakaway Kit Installation for Single and Dual Brake Axle Trailers
- Q&A: Wiring Diagram that the Ford Replacement OEM Tow Package Wiring Harness # 118243 Uses
- Video: MORryde Weight Distribution Hitches Removable Storage Bracket Guided Setup
- Q&A: Does 12V Pin on 7-way Trailer Connector Always Have Power
on Custom Fit Vehicle Wiring
Michael
3/12/2024
Where can you find the connection to the auxiliary lineunder the trailer