As part of bringing my Lycoming O-290-D2 into AD compliance, My A&E had the mags rebuilt at a shop in Ohio. When they returned, he reinstalled them on the engine and timed them. Today, after I hooked up the new Bogert P-leads, I was ohming them out to insure that I had the ignition switch wired up correctly when I  discovered that the Left mag was shorted to ground where the hex nut P-lead connects to the mag.I eliminated all possibilities other than something internal to the mag. What could cause that? The A&E mentioned something about a metal finger down in the bottom of the hole. Anyone know what that does? Could a shorted capacitor- the one that was supposedly just replaced - cause this problem? My logs are at the hangar but I think this is a S4LN-21 mag. Any advice would be appreciated, 'cause I'm getting real tired of going backwards on this project.