i bought a voltmeter today at autozone and had a few questions about it. 1. will the readings be the same no matter what 12v source i connect it to or does it just meassure that accessory? 2. i plan on getting two add-a-circuits. one for the backlight to the fuse for my headlight. and the second one i was going to connect the volt meter to so that it is on when the car is on. so windows or something but will that work if it is connected to the fusebox? and last i was thinking about mounting it above my headunit so i wont have to drill but any other suggestions for that?