I have a 2005 F-350 and my hubs are not engaging. I have tested the vacume lines and they are all in good shape. I have tested the solonoid and it works correctly and opportates the hubs when manually applying power to the center post and grounding one of the other post. My question is, is there a control module or a relay in this system? What makes me think there is, is the color coding on the wires from the swith to the solonoid are not the same.