As part of another project, I'm going to convert the Airstream end of the tow vehicle 7-wire electrical harness to the modern female connector. The following two diagrams are all that's needed to make the modification:
This schematic of the Ford tow vehicle interface shows the use of relays to prevent overloading of the tow vehicle switches and allowing for separate fusing of the trailer currents. There's some additional useful info in the table regarding wire sizes and expected maximum currents:
Zep