I have a yellow wire connected to my positive terminal on the battery what is it

sounds like someone added an aftermarket system like amp for stereo. trace wire to source and you will see what it powers up

I have a yellow wire (approx. 12-14 gauge) as well. I have a U-haul trailer hitch and a trailer light pack. VERY important in the 2002 to use the pack for trailer lights! Wire leads back to passenger side rear tail/turn/reverse light lens, where it provides enough amperage and triggers trailer lights from two bulb system to one bulb system. U-Haul still carries them as of a year or so ago. gARYJ