Hi Greg, Im in the same situation as you. Also V50. Looking for a solid solution to have a coolant alarm. I was thinking if you're concerned about over powering the 5V sensor directly from car battery why you just don't add a voltage regulator instead of bothering yourself with empty 9V batteries that have to be replaced again and again. Search KZfaq "how to reduce voltage 12v to 5v". Eventually i want this to build in car dashboard somewhere including audible alarm. What about adding a fuse for safety? Please post a list of items and a howto you did build this. Volvo not adding a coolant alarm is an absolute design flaw. I have heard some people actually transferred their screenwasher fluid sensor to their coolant tank. Don't know how but you actually get a message "screenwash liquid low" in dashboard. No audible alarm though.