Only the "wrong side", because traditionally, they were mounted on the left, however, there is no requirement that they be only on the left. I have seen a few where the gurney was mounted on the right hand wall. A lot of times, it would also depend on what side the rear loading door was hinged on. The body builders would build the car any way that the customer wanted. I have seen some cars that have the second side door hinged at the rear of the door, which makes it quite easy for the attendant to enter the vehicle.