Why won't a 1994 Mercury Trio start with the key but it will if you put power to the starter solonid ignition switch or neutral switch?

Just guessing here, but it sounds like you need a PATS key to start your car. (passive anti-theft system). I don't know if your particular vehicle requires one, look in the owner's manual. If you have the original Mercury key, it would have a plastic head containing a computer chip (transponder). Contact your local Ford, Mercury, Lincoln dealer and ask for the Parts Dept., or a help desk. Have your make, model and VIN number handy. If your car needs a pats key, dealer prices can be high, try getting one on ebay. You'll still need to go to a dealer or a specialized locksmith shop and have it programmed. If you find out that your car doesn't require a pats key, then I'd check to see if the ignition key tumbler needs replaced.