Ok, here’s what I found out and did to my 2017 Edge SEL.:
1) Contacted Ford, they stated disconnect the negative terminal from battery per OM. Don’t worry about other factory installed grounds (they are tied to the negative wire bundle). In otherwords you disconnect the negative terminal you have removed power to the car.
2) Had Blue Ox BX2657 baseplate and the new Blue Ox wiring harness (BX88334) for lights installed. Wiring harness gets ground through car (connected at rear of car near lights per installer) and coach wiring via 6 pin connector (it’s ground is tied to the car near the connector. Also car is technically grounded to coach via the tow bar assembly. +12vdc for tail lights is provided from coach via 6 pin connector not the +12vdc from car battery. New wiring harness works perfectly with LEDs.
3) Had a negative battery terminal disconnect installed between battery ground wire and terminal post. It’s one of those screw knob type. The only issue is that the negative terminal is kind of far back under the hood and it’s al little tight to get my hand on it. I may install an on/off switch type later. That will require getting an extention negative battery wire to mount the switch in a more accessible location.
4) Installed dedicated 12vdc plug to run power from car battery to RVi Brake. Called RViBrake and asked about battery drain and if I needed a charge line to battery from coach. I informed the tech that I needed that on my 2013 Ford CMax. The tech said no need to run charge line. The battery is of sufficent size to not drain dead while towing (RVi Brake uses minimal voltage draw on battery). CMax required charge line because the starter battery was very small, as in most hybrids, it is only used to start the car then hybrid batteries take over. RVi Brake has a charger, it has only one line in (+12 vdc from coach) and 2 lines out (+/-12 vdc to battery posts). The reason for only one line in it that it takes ground from the car (as noted earlier) ground is also tied to the coach. (It assumes the car ground is still connected to the battery). In this instance you would be required to disconnect positive terminal from the battery instead of the negative terminal.
Now here’s where it gets “gotcha”: Ford says disconnect the negative terminal ( in OM). Technically you are removing power from the car by removing the positive terminal instead. Both methods will work according to Ford and RVi Brake, but it is not per the OM (warranty issue?). Also, it has been stated to me that removing the negative terminal versus the positive terminal is safer for people (no accidental shorting yourself to ground).
For now I plan to run with my negative battery terminal disconnected per OM. If battery drain becomes an issue then I will explore installing a battery disconnect on the positive side of battery and leaving the negative side connected.
Edited to add: Hooked up car to RV, setup car per OM, drove around block a few times to set up RVi Brake sensivity, ALL AOK. No memory loss of electronics in car. Did have to push Sirius XM button on radio, because it defaulted to FM. Did not lose any channel memory.
I hope this information helps.