Why is the weather radar mounted on the left wing of the TBM? Weather radar is mounted starboard on the Pilatus PC12 or in the Piper Meridian/M600/M500. 

It adds drag to the right wing, thus a right yawing moment, and helps to counteract the slipstream effect and P-factor that tends to yaw the aircraft to the left.

So why is the wx-radar mounted port on the TBM ? (the propeller rotates in the same direction as the PC12, so it seems like the wx-radar only adds more yaw to the left)
After some detective work I have concluded:

In the TBM planes, the center portion of the right wing leading edge is occupied by the stall warning vane (or an optional AOA sensor in newer models). The two pitot tubes are located under each wing and landing lights are positioned at wingtips. This would leave the current location for the optional weather radar pretty much the only option available.



TBM 700C pilot information manual, stall warning vane description on page 7.15.1

Source for picture