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Author Message   Brcamera Tinkerer Username: Brcamera Post Number: 85 Registered: 08-2010 Rating: N/A Votes: 0 Posted on Thursday, May 12, 2011 - 07:15 pm:    You can check the Mg3 combination magnet easily by shorting the black wire connection to ground and releasing the shutter. The shutter should stay open until you remove the ground connection. Although, as I said in an earlier post, I have found the issue to be contaminated magnet surfaces in most cases. The Mg3 magnet does not get as much attention because it generally serves well and does not cause a problem like the Mg2 magnet, also on the bottom of the camera. In fact, Canon encased the Mg2 magnet in plastic while the Mg3 magnet is quite naked to the world!