This disclosure provides connectors for smart windows. A smart window may incorporate an optically switchable pane. In one aspect, a window unit includes an insulated glass unit including an optically switchable pane. A wire assembly may be attached to the edge of the insulated glass unit and may include wires in electrical communication with electrodes of the optically switchable pane. A floating connector may be attached to a distal end of the wire assembly. The floating connector may include a flange and a nose, with two holes in the flange for affixing the floating connector to a first frame. The nose may include a terminal face that present two exposed contacts of opposite polarity. Pre-wired spacers improve fabrication efficiency and seal integrity of insulated glass units. Electrical connection systems include those embedded in the secondary seal of the insulated glass unit.