There are different ways of going about this. I unplugged both my analogue fuel & temp. gauges & they both show up on the LCD screen & seem to be much more stable/accurate. I then plugged the power for the Garmin into the power supply for the disconnected fuel gauge in the instrument cluster. I could have used either, it doesn't matter which one you use really. Thats one way or you could run it back & hook it up to your battery directly, but I wanted a switched power source & using the power for the disconnected gauge works well for us & we haven't had an issue in almost a year now. Good Luck . . . . Dave & Teddy~