GFCI's show reverse polarity but appear to be wired correctly
Have an older home with gfci's that show reverse polarity. They appear to be wired correctly, hot on hot line, white on white line. I ran a separate wire directly back to the neutral of the panel and connected this to the line side neutral. checking voltage with a tester trips the gfci with the separate neutral connected but does not trip with the neutral in the box connected. I am puzzled by this and can't seem to figure it out. I have talked with a few electricians and they don't know. Has anyone had a similar situation? This house has had some "do-it-yourself" wiring done before by someone who did not know what they were doing so it may be a problem hidden behind a wall. I have opened other boxes and can't find anything. Any advice would be appreciated.