Wiring depends on if it's stock replacement harness, removed from a parts car or aftermarket.

I don't know what you mean by "This car had the file cabinet in the back". Perhaps it's a business coupe? They were available in both the Special D-14 and Deluxe D-17.
http://auto.howstuffworks.com/1940-1948-dodge4.htm

http://e-carzone.com/dodge/d-14_deluxe_d-17_special_1940/
Please post pictures.