You can find this information from John Sherbit-MOTOR MANUAL/MOTORALLDATA Distributor
You can find this at you local public library...........
On a 2000 Mercury Cougar : That's your Anti-theft system status light
When the heater resistor goes, your climate control fans will only work on the fourth setting. You can get a new resistor from any Ford Lincoln Mercury dealer, though they may have to order one.
Your thermostat is stuck open.
location of heater control valve on 2005 mercury marguis ?
where is the heater control valve
http://www.coolcats.net/tech/troubleshooting/heatercore.html
The best way to find the location of a part on your car is to go to Autozone.com Once there, create an account, add your car to "my vehicles." In search key in part you are looking for, to the left of the part you should see "View Job Diagram." Click on and a repair guide image showing location of part will come up. The diagram will show the climate control system for heater related parts such as the Blend Door Actuator, Heater Core, Heater Hose Clamps, Heater Motor Resistor, Heater Control Vavle, and Blower Motor.
What you may be experiencing is a blown resistor. If the heater only works when on 4, but not 3, 2, or 1, then it is most definitely the answer. If it is, there is plenty of info on this at newcougar.org.
Diagram for vacum line / heater lines for 1983 nissan 280z
Try this link http://members.tccoa.com/timb/Heatercore.htm its for a 94 Thunderbird but it worked for my 95 Cougar. It has description and pictures. It's a tough project, make sure you have help. Good Luck!
You prob have to replace the heater core