There are a handful of electrical differences you'll need to resolve, but those differences are far easier to "fix" than trying to mash an Explorere wiring harness into your B3000.
1) A/C controls are very different but only take a few tweaks and re-routes to rsolve.
2) Different PATS - The Explorer uses a Type B with a separate module above the glove box, the Mazda uses a Type E. But, only a couple wires are involved. Zip tie the Expo key inside the Expo transciever, wire both the Expo transciever and module into the 5.0's harness is likely the easiest and least expensive path.
3) The 01 B3000 uses its PCM and transmission for a speed signal, the '00 Expo uses its ABS so your mix has no speed signal at the moment. Adding a 2 wire VSS to the output of the transfer case is likely the easy solution but grafting in some of the Expo ABS is also an option