Why Cant I Put Tow Vehicle in Reverse While Connected to RV with Roadmaster Invisibrake Installed

Published 12/15/2017

Products Featured in This Question

Roadmaster InvisiBrake Flat Tow Brake System - Preset

(304)

$1380.00

Roadmaster Brake-Lite Relay Kit for Towed Vehicles

(762)

$52.02

Question:

I purchased a braking system to tow my 2017 Lincoln MKX behind my motorhome from you guys earlier this year and it works great. But I have a question. When I hook my car up to the motorhome I connect the tow bar to my car and then I drive the car in reverse to lock the tow bar in place. I know this isnt the normal way to do it but it works for me. Before, I would always connect the tow bar and plug in the power wire to the car and motorhome, then drive in reverse to lock the arms with no issue. Now, for some reason, Im not able to shift the Lincoln into reverse unless I unplug the power from the RV. What changed?

asked by: Bob

Expert Reply:

First of all you're correct, that isn't the normal way to connect a tow vehicle to a motorhome and I don't recommend it since that isn't how the tow bar or base plates are designed to be used. Instead you should connect them and then drive the motorhome forward making an S curve, when possible, to lock the tow bar's arms. But I think you already know this.

I looked up your order and you're using the Roadmaster Invisibrake, part # RM-8700, and the Roadmaster Brake-Lite Relay, part # RM-88400. A great combination.

The only reason plugging the Lincoln into your motorhome should keep you from shifting into reverse is if the motorhome is running and you have its lights turned on. With the motorhome's lights on the Brake-Lite Relay is engaged which prevents you from putting the vehicle in reverse. This actually sounds like a good way to test the relay to make sure it's working properly.

I'm guessing this is what you're doing. Mainly because your Lincoln has a push button start, and on such vehicles you need to turn the RV's lights on in order to activate the Brake-Lite Relay. So here's what I'm thinking is going on. You hook the car up to the tow bar and plug the wiring into both the car and the motorhome. Then you go inside the RV, start it, and turn on the lights. This engages the relay, as well as provides the trickle charge to the Lincoln's battery as per the Invisibrake's instructions. In doing so, you prevent the Lincoln from being able to be shifted into reverse.

Now, this isn't new or any different than it was when you first installed both parts. So there's no reason why it worked before and doesn't now unless before you weren't turning on the lights to the RV. So another guess is that you changed your practice without even realizing what it would do.

If any of my guesses turn out to be wrong just let me know and we'll go another route. I did speculate quite a bit. But I think this is why you can't shift your Lincoln anymore.