Okay, so I was right... it was way too simple. I'm using a Bosch relay that is a double throw. So instead of monitoring fan current (lots of amps) I am going to measure the other pole to tell me when the fan is off. Voltage on that line means fan is off.
Doing it this way, I would assume I need a pull down resistor? Since high means off, then I need to pull down (make sure it's 0v) when it's on?
I am regulating voltage via a zener diode. Would capacitors do me any good? Should I bother?