Parts Needed to Activate Charge Circuit of 7-Way of 2025 Tiffin Wayfarer

Updated 12/12/2025 | Published 12/10/2025

Question:

Hello I have a 2025 Tiffin Wayfarer and tow a 2024 Ford Maverick Hybrid with a roadmaster set up. Im getting 0 volts out of the rear 7 pin from the Sprinter and therefore no charge to the tow car. Hooked up to another RV all worked fine. I assume no fuse or relay to check, so a fault somewhere. Can a get a dedicated charge line sprinter to tow car? Thanks!

asked by: Alan C

Expert Reply:

Hey Alan, not every 7-way has it's 12 volt accessory circuit active so what you can do is use a kit like the part # RM-156-75 to provide the wiring and connections to activate this circuit. You would connect the 7-way from the RV battery back to the 1:00 pin of the 7-way through the breaker and you'd be set. Which tow bar do you have?

expert reply by: Jameson C

Alan C.

12/10/2025

Thank you! I have the Falcon 2 tow bar. Per Roadmaster the 156-25 Towed Car Charge Line kit installed but was not aware the 156-75 was also needed. Did Roadmaster just add the 156-75 to the kit list as the Mavrick batteries have been draining? Thanks again, happy holidays! Alan

Jameson C.

12/10/2025

@AlanC So the part # RM-156-25 is for the towed vehicle side of the equation. So it gives you a completed charge circuit on the vehicle that is being flat towed. It does not do anything for the motorhome side of the charge circuit which is why if that circuit isn't present you would need the part # RM-156-75 as well.

Alan C.

12/11/2025

@JamesonC I spoke with roadmaster and they suggested the Curt 7-Way Trailer Adapter for Towing Trailers with LED Light to get the power needed for the battery charge to the toad. Do you think this is a viable option? Thanks Alan

Jameson C.

12/11/2025

@AlanC Yes that can work. I don't believe that comes with wire long enough to run to the front but which one specifically did they recommend?

See All (4) Replies to Alan C. ∨

Alan C.

12/11/2025

Curt C57003 which etrailer has in stock

Jameson C.

12/11/2025

@AlanC hmmm did they explain how that would help? You're trying to charge the towed vehicle battery and this does not create that charge circuit.

Alan

12/11/2025

@JamesonC The Curt plug would fool the control module in the Mercedes that voltage would be supplied to charge the battery. I'm pretty frustrated, Tiffin says it's the set up in the mercedes, miswired or blown relay or fuse under the passenger seat or the tow car set up. Mercedes says it's typically licensing by the RV manufacturer. The set up functions when tested with another RV, voltage everywhere. No problem on a couple of trips, then battery drain in the tow car, replaced battery. Based on that I would suspect fue relay in mercedes. Appreciate any thoughts. Thanks Alan

Jameson C.

12/11/2025

@Alan Okay, my apologies now I understand where you are coming from. Sorry for making you explain it to me as I am sure that's the last thing you want to do when dealing with a frustrating situation like this. So the adapter will allow the charge circuit on the RV to sense a trailer connection so that it would be active and charge the towed vehicle. This is a similar problem that new F-150s have too so this is a familiar solution and I believe it will do the trick.