Please need help identifying cord found in engine bay

focusongina

ok so I decided to change my  air filter as I had just driven it 1000 miles to my new home in Texas. I don't believe it'd ever been replaced before and there had been an awful smell coming from the vents.. I thought a quick clean out and new filter would be the ticket... Well I'm sure it was however in the process of removing the cover I pulled out a plug coming from <UNKNOWN> it had clips to secure it going up and around the back of the battery. Now on one end of the cord which is RED is labeled T, and flipped over is labeled with the number 6.   Following the entire cord to the opposite end there is a plug for an outlet, which is covered with a cap. I feel like a moron since I still HAVE NOT been able to successfully reconnect this mystery cord to wherever the flippin he!! It came from! Thanks for any suggestions or playful jokes! 

Mr_Shiftright

Well that's the plug for the Focus engine block heater. It's pretty much for extreme climates. Most cars in the U.S. don't need it.

Video Focus Block Heater

focusongina

Thank you soo much Mr_Shiftright!