Our stepframe lowloader has a passive rear steer, it just goes with the flow and helps out.
There is a locking pin that drops down when the reversing lights come on otherwise it will snap round the wrong way and work against you.
If the wheels are not straight when you put it in reverse it will not lock. We have a switch to manually force the reverse lights, say you want to reverse in to the left but kick round to the right first, if you don’t think there is enough space to get the wheels straight before reversjng you switch it on to lock the steer so that as soon as you stop and reverse they are already locked.