1980, 720 rear lights

[The Newt]

I’ve got the drivers side tail lights/brake lights working unless I turn the headlights on so far. Now the passenger side lights all show power going to the ground even though lights only have three plugs. They are basic round trailer lights from Napa. Three wire plug lights and the ground is just separate. How does it show power to it when nothing is hooked to it? Is the power jumping across the connection in the light? I’m super confused and can’t make sense of it. The other picture is a piece of harness the previous owner cut out. I can’t tell if it’s mostly just for the stereo that’s not there or maybe something else? Any help would be greatly appreciated. The pickup has a flatbed and this is the view of the passenger side from the top  

[yenpit]

Are you working with a wiring diagram for the 1980 720?