Can I test a wire on my car to see if it's working thats not yet joined up to a switched live? It's a white wire that runs from my boost gauge, it should work or be wired up to a switched live. It's the wire that lights up my boost gauge but I don't have the light working, so I need to know whats at fault. Should I get power from this white wire at all when I turn the ignition on? I know the wire it's joined to on my car has power as I have just tested it. The boost gauge has it's main live and earth connected when I am doing this test. The only wire I have off at the moment is this white wire for the light as I can't get it to work. I have put my tester on it as it is now and started my car, and I have no power coming from this wire at all. Am I doing anything wrong? Is this white wire at fault for not showing power coming from it, or should it be joined up to another live anyway? Cheers