possible cause of high idle could be that your idle contol switch / valve has carbon build up on it. remove and clean with carburetor cleaner. let it dry completely before re-installing it. idle should come down if not it has probably gone bad and need to be replaced.
where is the obd connection point on a 1992 thunderbird OBD1 is usually under hood by battery
http://www.autobytel.com/content/research/index.cfm?Search=1992+thunderbird&Action=search&id=21928%3BABTL&Submit.x=0&Submit.y=0&Submit=Search
On a 1992 Ford Thunderbird : The gas tank is under the vehicle , just in front of the rear wheels
In 1992 the Ford installed manual transmissions in the Super Coupe ONLY, automatic was an extra cost option. Thunderbird, Thunderbird Sport, and Thunderbird LX, in V-6 or V-8 had automatic transmissions ONLY.
yes most MN12 Ford Thunderbird/Cougar parts as far as body will interchange
I just checked the owners manual and mine has an 18 gallon tank. 1992 Ford Thunderbird 3.8 liter.
On a 1992 Ford Thunderbird : ( both the 3.8 liter V6 engine and the 5.0 liter V8 engine have a timing CHAIN )
Most likely it is a bad thermostat. The switch on the radiator fan could also have failed.
AOD
on the thermostat housing
It is a recall. You should take it to a ford dealer. They will take care of it. Here is a link, that shows recalls for The Thunderbird. http://www.dealerrater.com/recalls/Ford/THUNDERBIRD/
I believe that is 210 horsepower and 315 torque