I'm pretty sure you can find trailer light wiring diagrams on etrailer.com. Almost all trailer lights are wired the same, and use fairly standard colors. Each light makes the appropriate connection to the positive feed wire of the right color. Usually ground or negative does not get wired back to the trailer hitch like the positive wire. Every trailer light harness I have seen uses white wire for ground or negative. The other colors for lights (positive connection) are usually green, brown, and yellow (only takes 4 wires for trailer lights).
The 7 wire plug has additional wires for brake, battery charging, and reverse lights (rarely or never used).
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time