Recommended Roadmaster Battery Charge Line Kit for Towed Vehicles Amperage Transfer at 12V

Question:

I purchased item RM-156-25 on 2/12/18 in order to charge my 2018 Jeep Wranger battery while being towed behind my 2015 Ford F-350 Superduty. This was necessary so that my Patriot II supplemental braking system will not drain the Wrangler battery on long trips. The Ford factory 7-way connector on the F-350 has the usual pin which provides 12 volt auxiliary power. The electrical cord on my Roadmaster Nighthawk towbar is a 7-way at the Ford to 6-way at the Wrangler. The center of the 6-way passes along the 12 volt aux power from the Ford 7-way. I mounted a 6-wire trailer connector item RM-910030-7 on the Wranger and am using the EZT20B E-Z Mount Tow light kit. I hooked up the Roadmaster Battery Charge Line Kit for Towed Vehicles and ran the wire from the center of the 6-way connector on the Wrangler to the battery on the Wrangler. Upon testing the wire at the Wrangler battery, it is only providing 3.5 volts while the Ford is running. My questions are: should the Ford factory aux power pin be providing a full 12 volts? If not, do I need to bypass the aux power provided by the Ford factory 7-way and install item 156-75, the motorhome charge line kit, which I assume I can run from the Ford F-350 battery?

asked by: David O

Helpful Expert Reply:

It is very normal for the 12V charge line on a vehicle to provide only the voltage that is being provided by the alternator that is not being used by the vehicle itself. The 3.5 volts is not normal but just 3.5 amps would be normal when the vehicle is running.

If you want the full 12V power, then you will need to run the # RM-156-75 which will give you 12 gauge wire and allow you to transfer 15 amps to avoid overcharging your Jeep battery.

expert reply by: Jason S