My experience with the flat-four connector is that it ALWAYS trips the BFWS and puts the light on the dash. PITA for night driving.

Four wires are ground, tails (one wire for both sides), brakes (one wire for both sides) and turns.

So they look for tapping into ANY tail, ANY brake, turns and ground.

There are ways to get around that, but generally they cost more. Worth it if you plan on lotsa towing. Worth it also if you consider that, for example, the current to light the brakes and tails all runs through the BFWS relay. With the trailer lights added, that puts more current through the BFWS relay. Solution is usually a powered system.

Good Luck,

Bob

:>)