I found this white wire with a large hole eye connector hangind down by the fan. It looks like it could fit on the battery, which post. The battery is all I've played with in the past few years. Everything works and it goes into the stock harness, wondering if it's for the trailer tow package. 2007 Dakota 3.7.

 

it does not look like anything I recognize to be stock from Dodge. I know that you said that it goes into the main harness, but does it look like it was just added to the side and just attached together or actually into the main harness and goes to a plug? if it does, we can find the plug and pin in the service manual and track what it should go to.