can anyone tell me where fuses for heater circuit are on 1997 f150 and what number.I have tried to find them all day.everyone says check the fuse but no one knows where they r.tks

 

Usually if you get a code for the heater circuit, it is the sensor that has failed.

 

already replaced sensor.When i bought truck i noticed the connection was melted on exhaust.not sure if shorted,Replaced o2 still getting codes,replaced again to make sure i didn't get a bad one.It says heater circuit so i was looking for fuses tks

 

Most Ford O2 sensor heaters through 1997 read about 6 ohms resistance.
Since 1998 they were changed to 3.3 ohms resistance to give quicker heating.
The two are NOT interchangable. Did you get it from Ford or did you purchase it from aftermarket which may have given you a "universal" type , and they don't work right.
The heater current is provided by the PCM power relay and is usually duty cycled to prevent over heating. You may need to get a good scan tool to check this out, especially if the circuit was shorted by burned through wiring.