1986 Ford F-150 truck starting issue

After sitting all summer, I finally got around to putting the rebuilt starter and new solenoid back into my truck. After hooking up everything(correctly I thought) I went to hook up the negative battery cable and it arc'd and started turning over. The key wasn't even in the ignition. I have the starter cable on the "M" side of the relay. I have the + battery cable on the "B" side of the relay along with the wire coming from the coil. I have the ignition wire on the "S" terminal(snap on). I also have a wire running from the radio to the "B" side of the relay. (Someones fix a long time ago) According to the slip of paper with the solenoid, I have everythng hooked up correctly, but I am not sure where to go from here.