Mercury Ignition Problems - Please Help!

[alarmingmerc]

I have a 2000 Mercury 50HP 2 stroke ELPTO, serial number OT097654 on a Bennington Pontoon. I bought the boat mid-2009 and used it the rest of that year with no problems. Late last year, I went to the lift to go out and it started up like normal. Just as it leveled out and was running smoothly it died. It roll over like crazy but not pop off. I checked everything (wiring, fuses, ect.) it had no spark so I left it a few days, tried it again and no go so I towed it in and hauled it to a local independent mechanic. It started right away for him and he tried it numerous times and it kept starting fine so I brought it home. I used it the rest of last year and all of this year and it worked great. Saturday night I went out on the lake and it worked great. Sunday morning I was going to take it out to put gas in. Same thing happened as last year. It started up, I backed out of the lift and it died. Rolls over like crazy but wouldn't restart. Checked everything again, topped the gas and oil off and checked everything - no spark. I called the same guy as last year (family friend and local well respected independent mechanic). He told me to unhook the black wire coming of the little control box to see if it would start. It did. Hooked the wire back up, it wouldn't. Took the wire back off, still wouldn't this time. Took it out of the water again and hauled it up to my house. Wouldn't start last night with the wire on or off. This morning it started right up. I just don't know where to start. I fear I am chasing a short or bad switch somewhere. It has never left me on the water, and I shut it off a lot on the lake, it always starts instantaneously when warm. Any help would be greatly appreciated.