Battery Heater Box
 

I am posting this here cause my truck was originally sold in MN. It is a 99 F150 Northland Edition 5.4L auto extended cab short box 4x4. It has a unique feature of an OE heated battery box. I am trying to find out how it works. The truck does not have a block heater so it does not work in conjunction with a 120V AC plug in type engine block heater. Can anyone in the Minnesota Chapter help. The truck lives in Wyoming now. Thanks.