There's a coupler in the rear differential. It's a two pin connector, so
I'd think you'd just need to figure out which is positive and which is
negative and wire to a switch. Check out the schematic at
www.hmaservice.com. If you aren't registered, you'll need to do that.
You'll probably then want to unplug the 4wd control module so it doesn't
turn on your malfunction lamp.
I don't recommend doing any of this. This can cause additional stress on
many different powertrain components and is likely to be met with severe
resistance on any type of warranty claim involving the transmission or