autozone.com try here type in you're vehicle info and follow the intructions. good luck.
find a chilton manual, they are cheap
autozone.com has repair resources including wiring diagrams.
Try AUTOBOOKSONLINE.COM If they don't have the wiring diagram separate they may have a shop manual
You can find this information from John Sherbit-MOTOR MANUAL/MOTORALLDATA Distributor
You can find this at you local public library...........
CID?
They are 5"x7" front ant rear, http://www.modifiedlife.com/1991-mercury-cougar-car-audio-wiring-schematic/
if you are trying to install the factory stereo to it...it should be the same plug...if you are trying to install the stereo for a cougar on a different car you need to buy the plug for that stereo and then a harness for the other car...
I am looking for a wiring diagram of a direction signal or flasher for a 1992 E150 Ford Van.
installer.com
You can find the wiring diagram for a relay position for a 1997 Mercury Sable in the owner's manual. You can also check local auto stores.
A grand marquis wiring diagram can be found in a Chiltons or Haynes auto repair manual.