Shifter linkage issue
 

My 98 shifter lever wouldn't go into park one day about 3 months ago, and has gotten to the point now that I can't start my car because I can't get it into neutral. I found a silver pin approximately 1/8 inch in diameter and a little longer than an inch laying on my floor mat that I can only assume is a connecting pin, but from where I can't say. It appears broken on one end. I can't find a diagram of the gearshift linkages anywhere. Can anyone give me some guidance?

Buy a copy of the Mercury Grand Marquis shop repair service manual for that year. That is the bible for the details that the generic repair manuals miss.
AllData is another good source.

My local community college has an auto repair program and the library has an online AllData subscription.