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Installing Tow Ready Battery Isolation Solenoid Downstream from Trailer Connector


I have an enclosed, single-axle cargo trailer with a 4-prong connection. I would like to install an auxiliary battery in the tongue box that will power interior and exterior flood lighting while the tow vehicle is not running the additional interior/exterior lights would be on a separate circuit from the manufacturer’s original lighting. However, I would like to charge the auxiliary battery while the tow vehicle is running using the isolation solenoid as described in a previous post. Would I be able to convert the 4-prong to a 7-way and then tie in the solenoid downstream of the plug? You guys have a great site and great customer service and tech support. I appreciate your help.


Helpful Expert Reply:

You can convert your trailer connector and mount the Tow Ready Battery Isolation Solenoid # TR118665 downstream from the plug. One place the ignition power post could be connected to is your trailer's running lights. If you tie in the ignition switched power post into the running lights, then your running lights will need to be on for your battery to charge. I called Tow Ready to double check, and they verified there would be no issue to mount the solenoid on the trailer and tie into the running lights for the switch.

To convert your vehicle end connector to a 7-way, I recommend using the Hopkins Adapter 4-pole to 7-pole and 4-pole # 37185. This connector will plug into the 4-way flat connector already on your vehicle, and provide you with wires for the 12 V auxiliary or reverse lights, brake controller, ground, and 12 V power source. You will need some additional wire to reach your vehicle's battery, you can use 10 Gauge Primary Wire # 10-1-1.

In order to have the 7-way connector on your trailer, I recommend using a 7-way connector with pre-connected wire leads, like # H20046. This Hopkins connector comes with 8 feet of wire to provide you with ample room to connect the wires to your current trailer wiring. You will want to cut off your existing 4-way flat on your trailer to install this 7-way connector. If you need additional wiring to connect to the solenoid and battery, you can use # 10-1-1 wire.

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