what is a good wire to tap that only carries current when the ignition is on? i need it to for air/fuel gauge. i have the other wires set up, and i was going to do the cigarette lighter wire, but i was told it was the red one, and there were two red ones, a plain red and a red with like gray stripes. i tapped the solid red and that didn't work. any other wires that would be easy to access?