Why would a motion sensor cause the light to flicker?

I recently installed a motion sensor light and was called back because the light was “flickering” at half brightness rather than staying on brightly. I tested the power and found good voltage, but when I put my tester to ohm meter and touched the white wire and the conduit, it showed that there is a connection between the two. At the panel there is no separation between the ground buss bar and the Neutral bus barr. Touching the two with ohm meter shows the same as when I touch the neutral and the conduit–a direct path between the two. I am unsure if there is a ground fault that caused the light to act that way, or if it is a bad motion detector. I bypassed the motion detector and wired the black and white wires I installed directly to the lights and they work fine. I wonder if the motion sensor is not turning itself off completely, or if there are more significant problems. I tested other outlets in the house with the ohm meter. I put one pin into the large neutral slot of the outlet and the other pin to the conduit or metal jct box and found the same connection between the neutral side of the outlet and the conduit.