Hello, I am looking for information on my boyfriends 1940 business coupe I would like to know how to research the title by the vin number and the best way to mount a fuse panel for the new wiring so it can't be that noticeable. This car had the file cabinet in the back I think that is the d 17 but my boyfriend thinks its the d 14.

The engine number, if it's the original engine, will tell you what it is.

A D is Dodge, I'll assume it's a Dodge.
A google search came up with this
"the VIN is on the driverside firewall, stamped into a ID plate that is held on with screws."

Now, before you run off to the DMV, remember that the term "VIN" or vehicle identification number didn't start until much later. Some states and some clerks used different numbers, which is why you want to check the paperwork to make sure it matches. Some places used the engine number. Most used the serial number that is on a tag on the driver's or passenger's front door jamb.
The big tag under the hood is NOT it.
Here's a link.
http://www.t137.com/registry/help/partspages/SerialNumberGuide/index.html

I printed out the pages I needed and took them in. The clerk was happy that I brought an extra copy for their use.

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.