A correct hypothesis test?
 

I thought I had a bad oil pressure sensor. Bought new one but could not get old one out, so took it to my mechanic. He told me that there is nothing wrong with my oil pressure sensor becase he tested the resistance of a current through the sensor and said the resistance varied with rpm. He suggested I look for a grounded wire to the sensor. To test this hypothesis I ran a wire directly from the gauge to the sensor. Nothing changed, though the needle flickers when I touch it to the gauge contact. The gauge still pegs at 4 when I turn on the ignition and does not vary with rpm. Should I try running a hot and ground wire directly to the gauge?