When I was equipping my pickup to tow a boat, many years ago, I did what any upstanding engineer would do: I looked up the SAE standard electrical connector for trailer applications, so I would be interchangeable with other trailers.
I found a plug/socket pair that met the spec and installed the socket on my truck, and put the plug on the trailer.
But I have never seen another one like it -- when I was at a huge RV and trailer place in the panhandle, mechanics were calling each other over to look at the odd connectors.
So much for SAE standards.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida