You want a or some electric sparks going from one knob to the other, you can use some emissive media with a good amount of turbulence. Have a sharp color_map blue-white in the middle, clear everywhere else, turbulent cylindrical pattern, add some other small dimer tighter media to do some forking. Render using radiosity and the sparks will light up your cene.

 

Ok, I got this far, but I get an error when I run: Attempt to malloc zero size block

 

#declare Spark1 = object { sphere_sweep { b_spline,
                       & nbsp;           &n bsp;       3, //NUM_OF_SPHERES,
        &nbs p;             ;                      <-0.5, 0.0, 0.0>, 0.001 //CENTER, RADIUS,
          &n bsp;           &nb sp;           &nbs p;       < 0.0, 0.5, 0.5>, 0.01
            ;                         & nbsp;      < 0.5, 0.0, 0.0>, 0.001
          &nbs p;             ;                  }
           &n bsp;           &nb sp;   scale <(1 * Inch), (1 * Inch), (1 * Inch)>
                       & nbsp;  }