This paper reflects on the difficulties students have in understanding, designing and constructing electrical circuits through an analysis of errors they have made in drawing wiring and circuit diagrams. Prior to wiring a model house, a sample of 114 primary school teacher trainees were taken through a programme of instruction in current electricity designed to effect conceptual change. As part of the programme, students were asked to design both circuit as well as wiring diagrams for a doll's house. The wiring diagrams were then compared to the circuit designs and common errors in the circuit diagrams, the wiring diagrams as well as subsequent examination responses to related questions were recorded and categorised according to alternative models of electric current identified in the literature. In this way, both the circuit diagrams as well as the wiring diagrams were used as diagnostic instruments to identify preconceived ideas about simple DC circuits. An analysis of the catalogue of common errors in the circuit and wiring diagrams, suggests that students not only revert to earlier, non-scientific models of thinking about electricity when confronted with the rather more difficult task of spatially organising the components that need to be connected to fit in with the design of the house, but that they also exhibit interesting "transitional" diagrams that incorporate conflicting ideas about circuits. These instances of transitional thinking as manifested in the students' wiring and circuit diagrams might reflect instances of intermediate developmental models used by students, or perhaps the re-emergence of phenomenological primitives. This conceptual ecology that is manifested through a process of designing wiring diagrams could be a useful way to track and facilitate conceptual change in students.