I’m using a 4 wire boat trailer harness. I terminated the chassis wiring in a typical 4flat car side. The. The bed uses the trailer side wiring and color scheme. I went with the boat trailer harness because it splits the tail into 2 separate browns at the connector.
To add trailer lights ypu can get a 12” 4flat extension and T off of that to a second trailer connector at the hitch.


Pat
1940’s tech was great in the 40’s