This is a tough problem to identify a solution for. I was asked to replace a halogen bulb in an outside, row home fixture, and I know that it worked the week before. When I installed an LED then a CFL bulb, in daylight, it did not appear to be ON, until I accidentally touched a ferrule nut holding the fixture to the wall. Then the LED and CFL came on fully, OFF when I let go or when I touched any other of the fixture. All surfaces seem to be painted or conversion coated. When I installed an incandescent bulb, nothing happened with or with out touching the same nut. I have yet to try a replacement halogen bulb, as if that might be the solution (need to borrow a ladder again) The only other point of information, is that the house was refurbished less than 8 years ago. In keeping with the NEC, they back filled the ground (3rd) pin in the electrical outlets, as they did not carry a ground wire to those outlets. I assume hot & neutral are in the lamp's switch box, as I see both white and black Romex wires. Any suggestions?