Normally there is a regulator and wires running underneath the pillon seat.  If I understand correctly at least some of the wires run to either the rear signals or tail light.  Since there are not any visible wires in your pic, it may be that the previous owner moved both the regulator and the wires already.  The regulator is relatively simple to move and can be tucked in other places (like under the rider's seat).  The wires are harder.  It should be easy to take your pillon seat off and find out.

Thanks Greg.

I managed to locate the correct bolts and got both seats off.  I discovered that the pillion was not installed correctly, one of the plastic clips on the rear of the seat was outside the bracket that holds it down.

The regulator is still there, and all of the wiring.  It looks like this will have to be a winter project - more involved than a beginner like me should tackle right now.  I assume the regulator is that thing that looks like a heat sink.  What heat does it serve to dissipate?  Something to do with the turn signals?  Please bear with me - I'm new at this.

Naaah, we don't need no stinkin' drummer!  

The pipe is a Kawasaki of all things.  Don't know what model - it was put on by a previous owner.