I am rewiring my old house (35+ years old) that had non-grounded aluminum wiring (very dangerous!) with good ol' copper/grounded wiring. I have four rooms done and in each room I have put in wall outlets that go to a switch by the door. When I finished the rooms, I used my circuit tester to make sure everything was wired and working properly and there were no problems. I have now gone back and checked the switched outlets with my tester and three out of the four rooms (the newest room does not have the problem) are now showing an "Open Ground". One thing to note is that the light on the tester does not illuminate brightly. The light is dull but still lit. When I turn the switch on, the tester says there is no problem. I have used my meter to test continuity between the ground bar in the sub-panel and the ground wire on the outlet that the tester is showing has the open ground. I have 0 Ohms of resistance so I know there is no broken wires so now I am really confused. Everything I have read says this is bad as it is a potential shock hazard so I need to get it fixed. I have checked and rechecked the wiring and everything looks fine. I have also gone as far as moving the outlet from the room that does not show the open ground to the room that does show the open ground but that did not work. The problem stayed in the same room so I know it is not the outlet itself. Can anyone tell me why the tester is showing an open ground? Where can I start to diagnose the problem. Thanks in advance for your help.