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Kit allows up to 15 amps from your RV's battery to be used to maintain the charge of your towed car's battery while the car is being towed. Charge line connects to the 6-way or 7-way plug on your vehicle. Requires separate charge line in RV.
Features:
California residents: click here
Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Hey, everybody. How's it going Today we're gonna be going over and showing you how to install the Roadmaster Battery Charge Line kit here on a 2022 Ford F-150. So a battery charge line kit simply put is gonna take the motor home's battery and charge the battery here on the vehicle while you're out in tow. Now, this is important because sometimes the vehicle battery can actually drain while you're in tow. So if you arrive to your destination with a dead battery, you're gonna need a way to fix that and that's where the charge line comes into play. That's gonna ensure you never have a dead battery when you get to your campsite.
Now, the design of this battery charge line is very, very simple. We're gonna first locate our battery into the engine bay which is over here on the passenger side, and then we're gonna attach a wire that goes to a circuit breaker. So our circuit breaker is gonna ensure that no issues with our vehicle affect our motor home and vice versa. So once we pass through that circuit breaker, we're pretty much just gonna trace the wire all the way down to the front of the vehicle where we have our trailer connector. And then we're actually gonna be attaching this to the motor home with the umbilical cord for our wiring harness.
So in order to utilize this kit, you do have to have a seven to six-way. So, unfortunately, four-way-only wiring harnesses will not work with this, but there's plenty of options for seven to six-ways. We actually installed a Roadmaster one on this one if you guys wanna check that out. And then here is where we have the battery charge line routed to on the front of the vehicle. It's actually just attached to this trailer connector.
And then we attach it to the motor home's battery with your umbilical cord as we just said. So there's really not much else to say about this battery charge line kit. It's very simple and it's gonna do its job. The only thing left is to show you how easy it is to install, which we'll jump into now. So first step of our installation we're gonna take our circuit breaker here.
We're gonna open up the hood of our vehicle, come over here to the passenger side because that's where our battery is and we need to find a nice stable location for this. And if we look inside just directly beside the battery, at the edge of the battery tray, we're gonna have a pretty good surface right there. So a nice flat surface that we can attach our circuit breaker to. So using the provided self-tapping screws that come in your kit, I'm going to attach our circuit breaker here to the battery tray. Now that we've got one in, and I'll go ahead and attach the other. So now that we have our circuit breaker mounted, we're gonna go ahead and screw off the nut on the bronze terminal, which is labeled bat for battery. So we're gonna go ahead. Be careful not to lose that into the engine bay. So we're gonna remove that and then we're gonna come here to the battery and uncover this rubber boot here to the positive terminal. So then in your kit you're gonna get some red wire along with some ring terminal. So what we did is we just went ahead and trimmed off a section of that red wire. On one side we have the large ring terminal. This is gonna go to the stud on the battery. And on the other side we have that smaller one that's gonna go to that post there. So I'm gonna start by attaching the post to the circuit breaker like so. Slide that over there and then re-secure our nut. So this is actually gonna be tightened down with a 3/8 socket. Once we get that nice and tight, we're gonna take an 11 millimeter socket and we're gonna be removing this nut here on the battery. So once we do that, I'm gonna take this ring terminal and attach it to that stud just like so. Then we're just gonna simply resecure our nut. Now, we're gonna take our remaining power wire and go ahead and crimp on our final ring terminal and we're going to uncover the silver screw on our circuit breaker labeled aux for auxiliary. So we're gonna remove that and then I'm going to attach this ring terminal to that stud and resecure our nut. And again, we'll resecure that down with a 3/8 socket. Now, keep in mind this is gonna be a live wire once we attach it to that stud. If you guys wanna hook this one up first and then the power connection to the battery second, that's totally fine. Now we're gonna route this from the engine bay to the front of the vehicle where we have our trailer connector located. So now you'll notice that I use some of the included wire loom just to cover up all that red wire. It just makes it look a little bit nicer here in the engine bay. But now we're gonna take this other wire. We're gonna route it along here, zip-tie it to this point here. Now, from here we're either gonna go straight down or we're gonna go to the other side. It's just all gonna depend on where your actual trailer connector is located. Ours is over there on the driver's side so we're gonna have to lift up this panel here and route it underneath. Now, with that being said, if we do have to go all the way to the driver's side, the included wire is not gonna be long enough. So you are gonna need to source some additional wires yourself if your trailer connector is over on the driver's side. If it's on the passengers side, just drop it straight down. But how we hit it on the driver's side is there's gonna be some pushpin fasteners here atop this panel. This is basically just covering the radiator. I just removed those ones along here and I propped this panel up. And then I just snuck our wire behind this. You can actually see it peeking out down through here. And I went behind the connector this way. That way I don't ever have to worry about it falling back that way. And then it's gonna come out to this location here. You can see our red wire down in there. And from this point we're just directly behind the taillight or the headlight rather. And we just dropped it all the way down and it's pretty much just gonna be routing behind the bumper here. And then we actually fished it out, this little area here where this pocket is. So this pocket is held in place with some clips. So we just went ahead and pry those out. And the reason I remove that is because this is where we're gonna be installing our trailer connector. So this part of your installation could vary a little bit depending on where you're installing your trailer connector or which trailer connector you have. But most of the time your battery charge line circuit which is the one we just ran is gonna go to the center pin of your six-way. So then once you do get that wire hooked up to the back of your trailer connector, that's gonna complete your look and installation of the Roadmaster Battery Charge Line Kit here on this 2022 Ford F-150..
I never knew I needed this for flat towing. Sales rep helped me pick the right item. Shipping was in a timely manner and the price was fair.
Ron
12/20/2025
The Roadmaster accessories work great - the brake switch in the car is ideal for turning it on and off as required.
Works great, I was having trouble keeping my car battery charged while flat towing. I have to keep my car key in the acc position and its electronics and the power brake has to get plugged in the car lighter eating away at my battery so when I stop usually around the second stop and restart the car the battery is dead. With this charge line kit my battery stays charged! It’s a win. I hope I explained it properly
Easy install. Especially when installing in conjunction with the towed vehicle wiring kit. This will keep your battery charged due to battery drain from the turn signal/brake/tail lights on your towed vehicle.
I had this professionally installed and it didn’t work the way I thought it should. When my tow vehicle was hooked up to my RV and the RV wasn’t running the Tow vehicles battery would feed back into the RV and the radio, back up camera, and GPS would remain on in the RV. This would ultimately drain the tow vehicle’s battery. I ended up replacing this with an RVi unit.
OVERPRICED AND UNDER DELIVERED!
You get about 15 feet of wire worth 50 cents per foot and it is BARELY enough to get from the front of the vehicle to the battery. It works, but just go to Homer Depot and buy a spool of wire and two circuit breakers and you'll have enough to wire both the RV and the tow vehicle for 50% less. Do Not Recommend
I highly recommend this if you’re towing your vehicle behind a motorhome. We’ve gone across the country several times in the past year and I’ve never had a dead (or weak) battery on my Toad.
Nick S.
10/13/2025
This is definitely a part that is often forgotten, but makes the biggest difference! I am glad it is working well for you. Cross country?! Have you had any favorite spots you have hit?
First off the chat rep sent me a complete list of everything that I would need to flat tow a 2015 Equinox so I made the $[XX]+ purchase from their list. After two full days installing all the items needed in the towed vehicle I try and attach it to RV and the connection can not be made. The tow bar will not fit into the base plate attaching points. I immediately (7/21) open a chat to let them know that they recommended the wrong parts and the rep agrees that a mistake was made and says that they will upgrade the shipping of the correct tow bar without charge so that I can have the tow bar a full day before my trip to test the complete install. I follow through with them after getting my order confirmation and it states that expected delivery is 7/22 so even though I needed to purchase a second two bar and wait for a refund on the first tow bar I am satisfied with the handling of the situation and comfortable with the full day to test the parts. On 7/22 I track the package only to see an expected delivery date of 7/23 so I immediately open up a chat and they proceed to tell me that there is nothing that they can do because it is already shipped. Then they go on to tell me that I agreed to 2-day shipping, which I did not. The previous rep told me that they would upgrade the shipping because it was their mistake. The normal Free Shipping is only a two day delivery to my area so an upgrade would mean next day shipping. I requested a full copy of the chat transcript to see where I specifically agreed to 2-Day shipping and they did not send me the transcript. I definitely regret giving this company my money. Their staff needs a lot more training to say the least. First they recommend the wrong parts so they are no expert in their field. Then they force me to purchase the replacement part fully knowing that the mistake was theirs. Then they can not follow through on their agreement to expedite the replacement part. Finally when confronted they proceed to put the blame on the customer as well as shrug their shoulders and say that there is nothing that they can do. Save yourself time, money and aggravation. Shop somewhere else where your business is actually appreciated.
The kit is fine. The install was for a 1997 jeep wrangler with a new roadmaster base plate. The red wire was approximately 12 inches short for wiring to battery. Had to buy red wire so I would have one piece without extra splice.
I ordered all the parts required to safely flat tow out 2017 Jeep Cherokee Trailhawk from etrailer.com. The only part they didn't have was the Mopar Flat Tow Enhancement kit Jeep requires to flat tow this model.
Ordering from them was great, the website is easy to use and I was able to locate all the pieces compatible with my specific vehicle. The expert recommendations help my decision choosing the right parts. I ordered from etrailer even though I found some of the parts on other websites a little cheaper. I chose to pay a little more because of all the effort etrailer has put into installation videos and guides. I was very pleasantly surprised to learn from etrailer that they have a price match guarantee!
So my equipment consisted of the following
Mopar Flat Tow Enhancement Kit (from Jeep)
Roadmaster Battery Charge Line Kit for Towed Vehicles
Mighty Cord 7-Way RV Style Trailer Connector - Trailer End
WesBarg 7-Way, RV-Style Connector w/ 6' Long Coiled Cable Trailer End
Pollak Black Plastic, 7-Pole, RV Blade-Style Trailer Socket - Vehicle End
Hopkins Custom Tail Light Wiring Kit for Towed Vehicles
SMI Stay-IN-Play DUO Supplemental Braking System
Roadmaster Brake-Lite Relay Kit for Towed Vehicles
Blue Ox Alpha Tow Bar - Motor Home Mount - 6,500 lbs
Blue Ox Base Plate Kit - Removable Arms
Blue Ox Tow Bar Cover - Aladdin, Aventa LX, Aventa II
The installation videos are great but not all inclusive. Take the time to read the instructions that come with the parts. This is a major project, I took about 30 hrs over a full week but as you'll see in the pictures I took s few extra steps to make a cleaner look.
Some of those extra steps:
The base plate install requires the bumper be modified cutting off a flange on each side, I spray painted this to prevent corrosion.
In the install video of the baseplate on the drivers side they use an extra quick link (not included) to run the safety cable around the wiper fluid reservoir. I took the time to remove it and run the safety cable behind it.
I didn't want our nice new vehicle to look like it can be towed so I played the brake away switch and 7 way trailer plug behind the license plate, so when not being towed our vehicle looks great!
Some things to be aware of. The Brake air cylinder that mounts to the brake pedal with four bolts may need longer bolts, it did on our Jeep. Spend the money for weather tight heat shrink crimp fittings. The Hopkins wire harness was about 1.5 feet short to get to my plug location. Buy extra zip ties, electrical tape and split loom.
I recommend reading all the various installation manuals and watching all the videos because the various components integrate together and if you install one at a time you'll be doing a bunch of extra work.
The brake light relay is a real pain in the butt, not because of the hardware but because of the location of the brake light switch which is very hard to get to.
Overall I am very happy with the products and how the installation looks. We haven't towed it yet but do not expect any problems.
Roy
7/30/2018
Still very happy with our purchase. We’ve towed over 10k miles and have had zero issues with our tow setup. I’ve shared my experience with several other RVrs and recommended your company for their needs. Thank you,
have successfully completed the installation of the following items that I purchased from etrailer:
> Nighthawk RM-676 tow bar
> RM-524458-5 base plate
> DEMCO Stay in play DM86VR
> RM-152 diode wiring kit
> RM-156-25 charge wire kit
> RM-88400 brake switch relay kit
I work slow but methodically. I had no issues other than the high degree of difficulty for a 68 y/o man working alone. This project exceeds the abilities of someone NOT mechanically inclined. There is also the need for some specialty tools. I found that feeding the wiring through the dash, firewall, and underbody was more difficult than installing the front baseplate. Overall, I am satisfied with the function of this installation. I am glad I did it myself rather than having it done.
Tow vehicle: 2021 Entegra Emblem 36U
Towed vehicle: 2018 Ford Fusion Platinum Energi
Jeffrey
11/19/2022
I have no regrets with this purchase. Items preform as advertised with no issues. I am very satisfied with Roadmaster and Demco products.
I’d highly recommend the charge line kit for anyone looking to tow for prolonged distances. No battery issues for me! Having the trickle charge gives me peace of mind as I tow. And one less thing to worry about is truly amazing. I used this for about 6 month on the road last year and am about to hit the road again. Love using products I feel confident with.
Victoria H.
3/21/2025
Thanks for your feedback Jenn! I'm happy to hear this adds more peace of mind to your adventures! Where to next?
Easy installation in 2024 Ford F 150 XLT, all required connectors and wire are included
Trailer people are the best! They assembled my replacement tow bar with this kit and it has worked perfectly ever since!
Brooke M.
5/9/2025
Right on! Where all have you been in the last year?
Easy to install, keeps my F150 battery charged up while flat towing behind my Motorhome
I purchased this as part of a package which included; Hitch and wiring for my 2022 Equinox, Base plate, Tow Bar, brake System and connecting air hose, break away cables, LED tow lights with wiring harness, and a trickle charger to keep the Equinox battery from going dead while I was towing it behind my class A RV.
I had etrailer do the install of all the components on my car and RV. All the workmanship was excellent and done in the amount of time they said it would take. Also because they did not have a video of this equipment being put on this year and model vehicle, I gave them permission to make a video(which added a extra day and a half to the install)and the installation was free. Everything has worked perfectly and I couldn't be happier. Etrailer is my go to for anything towing and also RV parts.
Jay
1/7/2025
I have had not trouble with battery on the Equinox which makes this all worth it. Etrailer lead me right
This product did exactly as described and was just what we needed to keep the battery charged in our towed vehicle.
Great service!
William
4/28/2025
This product has been working perfectly now for a year. No problems, thanks
I was told this would allow me to charge the battery on my 2025 Chevy Trax. You can only disconnect the negative battery terminal, not the positive battery terminal, so it will not work. Since the positive battery terminal is always connected and your motorhome provides the ground, you cannot isolate the battery - unless someone has come up with some sort of diode system.
It's working as far as I know. It was recommended by etrailer to add to my complete towing package. The installers put it in.I was glad for the quick helpful service fro etrailer when I asked questions about what I should get.
Good direction for installation easy to install.
Installation was straight forward no problems have not had a chance to tow our 2025 Maverick as I'm not done installing everything yet.
The Roadmaster brake connection kit has worked flawlessly on our toad. Thanks!
Richard
2/11/2025
Brake connection kit has worked fine with my Blue Ox system
The kit arrived without the fuse line. etrailer's excellent customer service took care of me quickly.
Brooke M.
4/4/2025
Glad we made it right!
I found out the hard way why I needed this. Dead tow
Vehicle battery when I was trying to go without this on the first trip.
Good instructions, easy to hook up.
Easy fast installation. Works as advert ised
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Victoria H.
1/9/2025
That's awesome Ron! I will let them know you reached out.