Voltage regulator

[fredM]

I was checking out my voltage regulator because I have Sunday off and I'm spending it with my Mercury. The amps gauge has a kind of a flicker to it and while trying to find out why I noticed that with the cover off the amps gauge works great. When I put the cover on the volts drops almost a half volt. Through trial and error, I know that the cover is not hitting anything. I went as far as putting a double gasket on to rule out anything simple. So, I put a plastic bowl on it and went for a ride. All is well but I don't want to have a bowl on the regulator. Is there any magnetic field I'm upsetting? Something else? Thanks.