so mine was totally independent from the front, I controlled mine through a toggle switch mounted on the trans shift lever, it was hydraulic powered from a p.s. pump but controlled the flow with electric silinoid valves to control the direction of the flow of the fluid. I did not build that rig, I bought it used the system was already in place, I did make some improvements to it but that's it.
I do think that a motor controlling a pinion on a rack could work, might have a large draw to it, not realy sure, the gearing of it might be tricky too. too fast and there wouldn't be any strength to it and to slow would be just as bad, not to mention what would hold it in place when you weren't trying to adjust the steering angle with the motor? if you were to hit a rock with the back tires and put a little side load on them what would stop them from just turning to go the path of least resistance even if you didn't want them too
