2000-2005 Mercury Sable-2000-2007 Ford Taurus Troubleshooting no start problem when battery is good

2000-2005 Mercury Sable/2000-2007 Ford Taurus Troubleshooting no start problem when battery is good: Battery tested good Dash lights come on but no start Replaced alternator but no start Checked all fuses but no start Replaced starter relay but no start Replaced fuel relay but no start Replaced ignition switch but no start Checked mega fuse but no start Checked starter and solenoid- starter not responding (Oil soaked, Had a burned smell) Replaced starter- engine started It took me a week the find the problem. (Starter had a burned wire smell which indicated it was bad, although I had it tested at a local O'reilly auto store after I took it off the car. It passed their test.)