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?
autozone.com try here type in you're vehicle info and follow the intructions. good luck.
provide wiring diagram for Avalon 2002
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...
They are 5"x7" front ant rear, http://www.modifiedlife.com/1991-mercury-cougar-car-audio-wiring-schematic/
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.