The symptoms you describe arent normal but might well not be what caused the engine to fail to start. But you dont give anything like enough information for me to be able to help. For example, when you say it wouldnt start what do you mean? Did the engine turn over but fail to catch? Or did it not turn? If it didnt turn could you hear a clicking noise from the starter motor? When you turned the key did any lights dim?
You should not have another wire jury rigged direct to the battery. There will be a terminal on the key switch for auxiliaries. If the power of whatever is currently connected to the battery is too great for that switch then the switch should operate a relay. Either way the feed should come from the fuse box.
The whining noise - is it engine speed related? If so then likely its from the alternator. Quite possibly just pick up from the way that the amp is connected.
