enblethen wrote:
They could have wired it for brake lights on a seven pin connector with separate turn signals. The seven to four adpater would not pass the barke lights.
There is no brake light pin on a 7-pin connector. It's for brakes, not lights. Unless you're suggesting they wires the 7-pin non-standard.
If the coach has a 7-pin connector it should already be wired from a conveter box that merges the brake lights and turn signals onto the 2 pins turn signal pins. Then the trailer (or magnetic lights) must have only red lights that use brake and turn as the same filament.