Note that depending on the supplemental brake system (such as the Stay in Play, which I use) used you might have to disconnect the positive lead from the battery. This is because a braking system powered from the battery can create a negative ground through the tow bar. The reason no power should get to the car?s systems is because you don?t want the ?little man? inside the dual clutch automatic transmission to shift the transmission out of neutral. The trans isn?t a normal automatic but actually a stick shift with a ?little man?, so to speak, inside who works the clutch and gearshift.
I contacted Ford and they OK disconnecting the positive rather than the negative in this case. When I get my 2018 Titanium Focus set up for towing a Stay in Play dealer will do it and install a solenoid switch on the dash to interrupt the positive lead.
So if you?re using an electrical supplemental brake be careful to investigate how it interacts with the car?s electrical system. I?m not saying that with your system you?ll need to disconnect the positive rather than the negative, I?m saying be sure.
I have half a mind to just go with a mechanical surge brake system but I have the Stay in Play from my previous toad and hate to waste it.