I have a '98 F-150 without the cargo lights next to the high mount stop lamp and when I had to replace the stop lamp, I noticed three wires going up to the stop lamp. I was just wondering what the third wire is for? Is this for some sort of floating ground? Thanks for any input.

 

this is what i show.

LG is for the stop light

BK/LG is for both cargo lights.

BK is for all three to ground.

and there is another connector near the laiht houseing. if you had another light assm you couyld just plug it in from there. good luck