98 SW wagon starts fine but stalls out when put into drive or reverse. Code P0743 comes up after diagnostic check. Says Torque Converter Circuit is open. How do I go about fixing this?

HI. This code is not necessarily a transmission fault code. You will need to check the engine sensors first before you replace any major transmission components.
The code(P0743),accompanied by symptoms of power loss and backfiring, indicates a defective mass sensor. To verify, check the mass air flow sensor for proper mounting, cracked air hose and dirty connecting air filter unit. Otherwise, check the mass air flow sensor supply voltage and ground voltage readings, as well. Before replacing it, service it using a brake spray cleaner. Once the mass air flow sensor is replaced and the code still shows up, then have the transmission tested for performance by monitoring the operating transmission pressures.
Here are a few connecting sensors that will play a part in inducing this particular code, as well.
A. Throttle position sensor B. MAP sensor C. Vehicle Speed Senor

During acceleration, these engine vehicle sensors play an important part in engine computer management dynamic functions during operation. These sensors must be monitored first, especially, when accompanied by performance problems such as hesitation and cutting out. However, if the transmission goes into limp mode right away (stuck in low gear), then check your transmission solenoids. Once you have verified that all sensors are functioning, then and only then, will you need to replace the TC switch.

I was definitely gonna say your torque converter. The fix is to replace your torque converter. The convertor basically transfers the moving motion from the engine to the non moving motion of your transmission smoothly. When it goes bad it will usually make the motor run rough in gear or stall the motor when it's completely bad. It will be a fairly expensive cost since the torque convertor sits between the engine and transmission. It also could be faulty wiring as well. You would have to have it physically diagnosed by a mechanic to confirm if its electrical or the actual torque convertor.