I looked at doing the opposite of this on my '96 a while back, here's what I remember.
There is more than just the wiring to the 4x4 switch on the dash, there is a TCC (Transfer Case Control) module on the steering column that you'd need as well. Also all the wiring is tied into the neutral/park switch and the vehicle control module, and I have no idea if any of would be the same between the two cases. And your biggest problem is you're putting this in a '95. That year is well known for having "one year only" parts (IE Transmissions/Heater Controls), so I have no idea if you could take the transfer case and associated wiring out of a '98 and install it in a '95.
Here's a wiring link to a '98 to give you an idea how much wiring you could be looking at.
http://www.gmtruckcentral.com/wiringdiagrams/1998/Electronic-Transfer-Case-Circuit.pdf
Also don't forget that these cases came in two different spline inputs, 27 and 32. The half tons got the 27 and the three quarter got the 32 (1 tons got a borg warner case).
Also, the NP243 is the non-Autotrac case, the Autotrac was the NP246, so if you have a case with AutoTrac it's not an NP243. I have no idea how the NP246 is wired.
As far as the wires behind the dash, I'm betting those are for auxilary lights of some sort. There were fog light switches that go in the same spot as the 4x4 switch (although I've never heard of any factory pre-wiring, idk on that one)
Bottom line if it was me, I'd be rebuilding the NP241. I'm not saying it's impossible to swap in the NP243, I just think it's going to be a ton of work and a wiring nightmare. Rebuilding the NP241 would just be much easier.
I hope that was some useful info. I did it all from memory so if I'm off on something someone please correct me.
