The temperature sensor is near where you are mounting the unit, and it is switched.
If you can go under the dash, tap the green wire attatched to the key cylinder. Thats the main ignition line.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>