found this but I learned real quick when I was changing the style of switch on my truck that a handful of alligator clip jumpers was my best friend. I got to make sure everything worked as ir should before making any connections permanent.  https://diagramlibrarymps.z21.web.core.windows.net/57-chevy-turn-signal-wiring-diagram.html

Can you include a picture? Maybe someone will recognize the brand. Also you might search eBay for a look alike that may have the brand name. Then you could google for a wiring diagram. Worth a shot.

Most seven wire switches are similar in regards to wiring. Wire colors may vary somewhat but the functions are pretty standard. I found this article to be informative. https://www.restore-an-old-car.com/add-turn-signals-to-an-old-car.html

The one I bought is similar to the diagram that is linked above has.  Before installing mine I hooked it to a 6volt lead and bench tested it with a series of four bulbs.  This way I confirmed it worked and that all of the listed colors were correct.  

I found this article on the stovebolt page.

https://www.stovebolt.com/techtips/turn_signal.htm

Make certain too the correct flasher relay is used.  NAPA EL 550 was found to work correctly in my install efforts.