On reading your post a second time, never bypass any safety switch. Just find out how to repair whatever problem you're having, but leave the safety switch alone. Yesterday at the hardware store, I just spoke to a guy who knew someone who bypassed the safety, and ended up injuring himself badly.
Have you tried calling John Deere, or visiting their website? Manufacturers often have repair manuals that will help with issues like this.
Alternatively, do a Google search for "lawn mower repair forum". There are several forums where you can register and ask questions like this.
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