What causes an open ground on a wall outlet when I turn on the light switch to the ceiling lights?
Ok John this probably not the answer you want to hear but, using a tester as you describe is fine for checking for problems, now is the time to call a electrician to identify and resolve the wiring issue.... most not all homes built around your homes era did not have grounded outlets. Please get a referral and try to avoid fixed price franchise electricians. God Bless Big Jim