I have not used Nikon so the below should be checked.
The Nikon D750 uses the MC-DC2 connector and looks to work by bringing the focus and shutter lines to ground the same as the Canon I have.
Since the MC-DC2 connector is unique to Nikon it would probably be better to buy a cheap shutter release cable and repurpose it. This will also let you check how it works to confirm it is basic contact switches.
Have a look at http://www.dropcontroller.com/cables-and-leads/. This is for Canon but it shows the inside of a shutter release and may give you some ideas of what to look for.
Not sot sure if this has the MC-DC2 connector but it looks likew you can get extension/adaptor leads that do not need modifying.
- This reply was modified 3 years, 4 months ago by Martyn.