On the "7 Pin" Trailer Wiring System

Common questions and clarification on the use of the 7 pin wiring and box.

OGT gets a lot of questions about the 7 pin wiring!     Our system is generic and industry standard.    The 7 pin plug should work with the trailer harness plug on all vehicles - if you have issues, contact your vehicle manufacturer with the dimensions of our plug and they will be able to help you.


Here is an image of the plug and of the box, showing the function of each pin:

7 Pin wire diagram

All of our lights on the trailer are LED, and the grounds come all the way back to this box for every run.     

Connecting the Auxiliary power pin to the trailer battery bank (if not already connected (pre-2022 production units)


The 10 AWG auxiliary power pin, black wire, is intended to and is already connected in order to charge the battery in the emergency break away box for the electric brake system. 


Some customers are using this aux. power pin as a 12v charge lead for their trailer battery system - connecting it to the 2x group 31 deep cycle batteries.  Since this wire is not specifically intended for this purpose, has a long run, and the vehicle side of the wiring is unknown (circuit breakers, gauge, capacity,) the charging of the trailer batteries via this method is best considered trickle or maintenance.     If your batteries are discharged to under 12.5 volts (essentially, not fully charged,) they should be charged by a DC to DC charger, an AC to DC charger (onboard or other,) the solar system c/w a charge controller, or by other means.   They can then be connected to the vehicle's 7 pin system.


A 30 amp inline fuse must be installed between the aux. pin and the house batteries if not done so at the factory.   A 30 amp breaker/switch can be installed inline between the 7 pin aux. power pin and the trailer battery system.   The fuse will protect the circuit and the switch/breaker. 


Grounding is equally important as the current supply.   The connection from the ground pin in the 7 pin box to the trailer battery bank should be checked and improved if necessary.     You can run a 10 gauge lead from the white pin in the 7 pin box to the ground bus on the bluesea fuse panel, or to the ground post of one of the 12v batteries.   With the only connection between the vehicle and the trailer being the 7 pin connector (IE: with the trailer disconnected and with the chains not in contact,) continuity should be confirmed between the ground pin in the 7 pin box and the trailer's frame.   If there is a high resistance here, it is recommended that a min. 10 gauge ground wire is run from the ground pin in the 7 pin box to the trailer frame.


All of these modifications must be vetted by the customer or their chosen installer and are not the responsibility of OGT!   


Consider that the tow vehicle's charging system is regulated to and capable of charging its own battery and also providing power for the rest of the vehicle.  The 10AWG wire is good for about 15 amps or less at this length of run and you will not have obvious control over the current flowing through it unless you install a fuse as mentioned above.  Some vehicles have fuses/circuit breakers on this branch at 40 amps.   Another risk would be discharging the vehicle battery or overloading the vehicle alternator which could spell trouble in remote environs.     Finally, if the trailer batteries are completely discharged, they will also want to discharge the battery that services the emergency breakaway system if there's no switch or a closed switch between the two battery systems.

Be careful, and have fun out there!

The OGT Team