Mercury OB 225 will crank, on spark with intermittent fuel pump turn on

[doradoscott]

2001 Mercury OB 225 has no spark to any plugs. It will crank but not start. When the key is turned to the ON position (not to cranking position) the fuel pump occasionally kicks on but there is no consistency with it. In the last 6 months we had an alternator change out and at that time did some due for maintenance listed below. A month or two after the alternator change out, while out and about, an alarm came on, nothing could be found to cause it, and when restarted it came on again, the boat hiccuped, shut off and when re-started again there was no alarm. It did this one other time and both times ran fine afterwards. Just recently it was not wanting to start when cranked, until finally it just would not start. A local merc repair/dealer reported the issue to us, after supposedly hooking it up to diagnostic computer, as the engine harness. We changed that, and the issue was not resolved. We then went ahead and changed the key harness and kill switch just to be sure since they were cheap, comparatively. Lastly, we had a new (certified) merc mechanic come to the house, and our computer (ECU) would not communicate to and would periodically shut off his diagnostic computer, we were given a used ECU to try before purchasing and we still have the same issue. Now the borrowed ECU is a 2003 so we're not sure if it's completely compatible but the same issue is still there.
Any help would be appreciated!

New: plugs, wires, alternator, engine harness, key harness, kill switch, thermostat, water pump kit.