The instrumentation has wires running along the outside of the body along with the wiring to run the motors and servos so all this is added at the same time.  Here are pictures of what look like rotational sensors on the corner wheels.  Some of the wiring is starting to be zip tied to the rocker/bogie arms.

I chose to use waxed tape to bundle the wires together.

The wires are then zip tied to the side of the body just like the real rover.  It makes sense to label the bundles of wires, either that or ohm them out later to figure out what goes to what.

The rear camera is easy.  The front pair of cameras and lasers are a bit more complicated.  First test fit the bar that holds them, then glue them on and finally attach the wires to a junction box.  I am holding off gluing this rather delicate structure on until I finish the wire interface board.

The outer wires go through a plate that has two sided pins.  These could have been soldered but I chose to make them detachable.  There will be a plate that covers the wires.  The inner cable harness attaches to the other side of the plate.  

I first tested the joystick and then the wheels moving forward/reverse.  The wheel motors are driven by two dual L298N motor drivers.  You have to make sure the wires are attached such that all four motors turn in the same direction.  After that I tried to get the stepper motors working.  They each use an A4988 Stepper motor driver.  All this worked fine in a bench test, however on the model these little stepper motors do not have enough power to pivot the wheels.  Stepper motors that have enough power to turn the wheels would be way too large and look wrong.  At this point I have decided to not implement the turning function.  The rover will only be able to move forward and backward.  Here is a picture of the interior.  There is plenty of room if you want to add additional functionality such as working sensors.  I use a L6808 to convert the 9V battery power to 8V which drives the motors.