Step 3: The lazy fix.
a bridge rectifier.
it's that simple really.
here look up and I'll show you a picture of it working like that.
did you see it?
now here's the reasoning, under normal usage a bridge rectifier changes ac current into dc, basically a back and forth flow into an always forth flow. so when you hook up a dc voltage to it all that the rectifier is doing is treating it like a normal ac voltage, and rectifying it to the positive and negative terminals. problem solved!