You need to ground that onto something a little better than a painted panel mate, you'd need to scratch the surface down to good clean metal to get a reading.
Do what Dave says and do a continuity test, have you got a circuit tester?
RedRaven wrote:I sat in the drivers seat and turned the ignition to on and I had the boot end of the cable that connects to the sender with a nail in it and touched it off the door arch but nothing moved on the gauge.