[Richard]

Hmmm, if your coach is wired like mine, you will find relays for the tail, brake, turn, and backup lights in that compartment.
Look on the inside compartment of the rear panel. Mine are clearly labeled.

So, that has two appreciable things to consider. One, is that the circuitry is already protected by those relays, and PLENTY of power is available for trailers and whatnot. Two, since the turns, brakes, and tail are separate the wiring is already EURO or four wire style. The converters were put on there to convert backwards to a three wire setup for the trailers.

If you have the relays, then the Hopkins device is redundant.

You have to decide whether you are going to run your dolly and trailer lights, three wire or four wire. I originally wired my tow car the old school three wire where the turns are incorporated into the brake/tail. I have all kinds of issues with drivers acting as if I weren’t giving a turn signal. I rewired the toad with a four wire setup so that I now blink the yellows on the toad. The turn signals are now what people are used to seeing. If you decide to go old school or three wire you will need a 4 to three converter.