I was replacing the left fender on my 02 2500 and while taking out the battery tray I discovered what looks like a plug in the bottom of the tray itself. I thought at first it was just plugging a hole but it has wires running to it from the harness by the headlight. Anyone know what that is for? I am very curious to find out.

 

Temperature sensor to detect overcharged/overheated batteries.

 

oh really, is there a light it activates?

 

No light to my knowledge, just interfaces with the PCM.

 

Sport headlight bundle prewired in many of the trucks, but you need the guts in the Power center behind the battery to make them work.

 

I am not sure if this has anything to do with the headlights as it actually runs two wires to the bottom of the battery box, unless I was not paying attention it looked like a plug of some kind. But now that you mention that, I have access to a parts truck (Durango) that has the Drv lights in the bumper. Is that what you refer to as Sport Lights? What will I need from the donor truck to make em work? The Durango has a Different headlight switch to activate so not sure if that would work on the Ram

 

It's for sure the battery temp sensor.
On some years it's on the driver's side.
Sometimes people run into charging problems if they use a shorter than stock replacement battery and use a spacer to make up the difference so that the hold-down bolts work.
The sensor has to be in contact with the bottom of the battery.

 

No, the driving lights are a different light.

The "SPORT" headlights are a quad beam designed headlight package offered on "SPORT" models. The standard is a sealed beam looking single bulb design. The "SPORT" has a separated hi/low beam designated by a clear lens with no dispersion bumps, like most newer cars and trucks have.

Look for a 2nd gen "SPORT" model with body colored bumpers and grille and you will see what I am talking about.

 

So this Durango is no where close to the Ram then, other words nothing will fit.