It seems you can't connect, say a normal lamp to an insulated wire. It seems to work with ProjectRed items however. Attached is an image

not sure if this is the case or not. insulated wires will not power the block it is sitting on. It also will not be effected if their support block is strongly powered.

That behavior is intentional, normal redstone dust does not connect to lamps (visually), therefore only indirect open air power works. If you want to connect it insulated, put another cable on the lamp