1966 Mustang coupe has been running great. Replaced my battery and now problems...I traced a bad wire to a yellow wire running from my starter solenoid to this box (pictured below). The yellow wire is going into where it says "s" and is directly above another yellow wire that says if the wire is used for anything other than radio suppression it will cause electrical failure. Might there be a bad fuse in this box? I am getting 12.5 V to the starter solenoid but when I turn on the ignition I don't even get a click. Nothing at all. I checked the voltage on the opposite side of the solenoid and it is showing 0. So the current isn't making it through the solenoid thus no power to starter which is why I feel like there is nothing when I turn on ignition. Either way, the bad wire was tested. When it gets juice my ground all of a sudden has the 12.5 V. If I then connect my ground cable back to the battery I of course get lotsa sparks. There is no chafing on the wire between the solenoid and the box pictured. So I assume something has to be awry inside this box. Before I open it and look inside I wanted to see if I could get any input from you all. Especially, what the heck this box is!