On the topic of 12V vs 5V.....

the fan will definitely put up with 13.8 and even a little more like the car might put out...

The DS1721 has a resistor with a 5.1V zener diode.. so in a sense, it has its own 5v supply.

As I mentioned, I used the +12V pads that are in the back corner next to the coax connector for external power. They're in parallel with the power input from the sled connector. Thus, the fan will operate when plugged into wall or car.

Enjoy.

p.s. my Image editor for windows seems hosed... might if I borrow the one you posted Loren?