How to install a 12 Volt line going from motorhome to towed vehicle

April 08, 2021, 11:45:58 am

I will be towing a 2013 Ford C Max Energi for the first time on April 12. I have a Roadmaster Blackhawk 2 tow bar with the Roadmaster base plate on the Energi. I purchased the wiring kit with diodes from Etrailer. It came with a 4 pin connector which is mounted to the front of the car. I have a 6 pin connector on my 2004 U320 4220. I have a 6pin to 4 pin adapter that I have on the mh. I hooked everything up and it works just like it should. However, being a newbie, and not very mechanical, I found out my car battery will discharge during towing and to rectify that, I need a towed vehicle battery maintainer.
I've have obtained a BrakeBuddy battery maintainer and the installation seems simple and straightforward on the towed vehicle side. What I need help with is how exactly you install a 12 volt line going from the Foretravel to the red wire on the BrakeBuddy. I realize I need to have a fuse or relay on this 12volt line. I need "Instructions for installing a 12 volt line for Dummies".
I have lifted up my bed(it goes sideways in the bedroom) and opened up the Cummins engine hatch to look for possible sources to tie into. I am not sure and do not want to do the wrong thing.
My 6 pin connector on the Foretravel has a middle pin that I believe is auxiliary and could be used. However, that forces me to get a different wire harness from the MH to my tow vehicle plus install a new plug on the car. I prefer to keep it simple and just run a 12 volt wire from the motorhome all the way over to the car and connect it to the red wire on the BrakeBuddy. I do NOT have a braking system on the car and do not need one for where I travel.
I simply want to know the step by step procedure for getting this to work.
I am open to any suggestions on my situation.
Side note: I bought another maintainer called the Toad Charger from LSL products. It would not arrive before I leave so I had it shipped to my destination. Maybe I should not worry about the battery going dead on the Energi?
Can you use the 2 jumper cable posts on the back of my Cummins to jump my Ford Energi?
I apologize for a very lengthy post.
Anyone know towing procedure for Energi? In neutral, but Accessory or off?

Re: How to install a 12 Volt line going from motorhome to towed vehicle

Reply #1 – April 08, 2021, 12:33:21 pm

Sorry I don't have a clue about towing your particular car.
But as far as getting 12 volts out to your car that's not an issue at all you have plenty of places in the engine compartment that you can pull 12 volts from. For instance you have a light in your engine compartment that should have 12 volts go into that. You can pull off of that. But in order to do something like that you have to know how many amps you're going to be drawing. Probably the best thing to do would be either to come off your start battery. Make sure you properly fuse it as close to the battery as you can. Run the appropriate gauge wire to your rear bumper and come off of that. You can tape it to your existing wiring harness.
I don't have that problem on my Jeep Grand Cherokee. All I do is put it in neutral and then shut everything off. It's an electronic neutral which is a pain in the butt at times but if you do the procedure properly it works each and every time. Definitely check your owner's manual for your vehicle to see about flat towing and if there isn't any mention then you might want to call the company.

Re: How to install a 12 Volt line going from motorhome to towed vehicle

Reply #2 – April 08, 2021, 12:39:23 pm

Best wiring to charge toad battery:

Fuse at both coach chassis AND toad battery. Fuse sized to protect the gauge wire you use

Recommend 8 gauge wire all the way.

IF (up to you) you want to only have it charging when the coach is running, use a 40 amp RELAY that closes with ignition source (easy in engine room).

Be sure to size the ground/negative wire the same as positive.

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