I don't know from your question which wire you are talking about, but I have this iron and one power cord wire goes direct to the middle terminal, the other ties to the blue wire going to the sealed power control unit. the power unit brown wire goes to the middle terminal and it's black wire goes to the right most terminal. The light's wires go to the right and left terminals. Hope this helps.
I know this layout because I am troubleshooting mine- it needs a new power control unit - - anyone know where I can get one???
DP, July 2008