Now I think I have it but I'm sure I need a diode but the question is what size and which way to point it.

 

hm...idk...

 

I gues it's trial and error time

 

yea, i would've gotten another switch and then wired the power and grounds through it, if your way works though, that'd be cool

 

a QPDT (quad pole double throw) will work but I can't find one around my electrical stores, at least a small one to install that doesnt have a monstrous switch.

 

you couldn't just use another dpdt and then flip both switches? i guess i'm not just understanding what the diode is going to do

 

I'm just afraid of shorting out the head unit in the processes of switching between the two USB devices. I know I can just power down the unit but its also a safety precaution. With the diode will keep the flow in one direction.