Ian,
Sounds like standard MEP circuiting. Pick your objects (receptacles, lights, etc.). Pull up the properties box. click electrical properties. Under connector properties, select the panel and circuit number of your choice. after devices are circuited, use the wire command to wire up.
(all this is contingent on your system and wires being already properly set-up and your existing symbols are MEP not standard acad blocks.
Hope this helped.