Programbo

I'm going to ask a very vague question just to spare everyone the extremely long details of why I want to know...I have a 1994 Cherokee with the 4.0 inline 6..4 speed auto...When I start my Jeep and it sits there idling, as soon as I shift into Reverse (But am not moving yet, foot on brake) what sensors/electrical components/etc are brought into play just from that simple act?..I know once you start to move more would come into operation but just sitting at idle how many things can anyone think of of an electrical nature that would be affected simply from shifting into Reverse?..Thanks