6v6gt:
To help make the points a bit more concrete, I've tried to draw a schematic based on my interpretation of what you have said.If the fan has only a small power requirement (mA), this may work. Does it look like what you want to achieve ?
Click to enlarge, depending on your browser:
Thank you so much for the effort. I really appreciate it. The schematic that's almost what want. Except for the vin part. I'm gonna need to borrow your schematic and edit something. Your schematic given me an idea on how the vin pin works 