The theft light on my 2001 Mercury Sable keeps coming on. At first it just bogged down the engine but it got even worse and it made the car stall. Eventually it stalled and would not restart. My mechanic replaced some frayed wires and a pcm relay. It seemed to work, the car was running again but within 24 hours it did it again. Any help would be appreciated.

SOURCE: serpentine belt roouting

here you go

SOURCE: CAr Stalls engine temperature warning light turns on

Next step is thermostat

SOURCE: Car not idling adn stalling when it is cold

sounds like the idle control vale is sticking when it is cold. It is located on the throttlebody right at the air inlet

SOURCE: theft light

That is normal, they all do this. it won't drain the battery.

SOURCE: i have a 2001 mercury

Yes, keep it disconnected for at least 10 minutes. Also make sure your Battery is good. Sometimes the Anti-theft is sensitive to Battery voltage and will not connect the internal parts to allow a start.

If you have a Keypad, enter the Security Code on the Keypad and turn the Ignition Key within 5 to 10 seconds to start it.