X6 Sq problem

[bronco]

I just bought an X6 sq from somenone who stopped the hobby. I switched my electronics from my b4 into the X6.
When I first tested it with my electronics the motor (Graupner Dr. Speed) was spinning but the diff outdrives weren't. I switched motor wires and only one combination makes everything sping correctly except in the wrong direction.
I put back the motor that came with the car (Losi 6.5T) and there was no problem (same speedo, same sensor cable, no changed settings).

Does anyone recognize this issue ?