I purchased a small volt meter that has a positive and negative wire (picture below) and want to hook it up today. I pulled the front dash with the fuel and temp gauge and put the positive on the light wire of the fuel gauge and can't find a good ground hook up. I touched the ground wire to several screw holes behind the dash and also to two of the nuts on the back of the fuel gauge with no luck. If I touch the ground wire to the ignition switch where the key goes in, it will work. I have the ignition on as the light wire works off of ignition, but am really confused why I can't get a good ground anywhere behind the dash. Would one of the other 3 wires running into the fuel gauge work as a ground even thought I tried the nuts on the back of the gauge. Suggestions appreciated, I want to finish this today. Thanks. I thought I knew a little about wiring, but this one has me stumped, call me stupid.