I'm not sure if this is the solution for you or not but, it sounds similar to my situationa fcouple years back. I had a problem w/my 4x4 kicking in, it would click like it was trying then cut out. After hours & hours of checking eveything possible, I finally found it inside the security torx asseblemed plate on the 4x4 shifter motor. The way this thing operates is by electrically positioning itself in the correct position on the circuit path (this is obvious when you see inside it) well it has a start point 2wd & a stop point 4wd. It is stopped by the metal pin that "should" have a plastic lining around it. In my case the plastic lining was deteriorated and broken into many small pieces. I simply found a piece of hard high pressure air tubing that was the same Inside diameter of the pin & the same thickness of one of the pieces of plastic found inside the cap. I put this over the pin & cut it down to be flush with the top of the pin. I was testing this by hooking up a battery to the motor to engage it, using multimeter jumpers to the correct pins. It took a few tries to find the correct pins but, so long as you don't leave the voltage on there you should not do any damage if you touch the wrong pins. One was for forward & one for reverse. It's ,much easier to test this when it's not installed in case and the cover is open, you can watch the motor work. So, in all besides time included it cost me a total price of $0 for a piece of tubing where the dealership wanted to sell me a new motor for some crazy ass amount. It's been a while since I messed w/it but if you have any questions feel free to drop me an email. Good luck
