Jeep Repair: Service 4WD Switch on 1995 Grand Ch., powertrain control, vacuum switch

Question
I have a 1995 Grand Cherokee Larado 5.2 automatic.  Full time 4 wheel drive trans and my transfer case says it is a 249.  Recently the "vehicle information center" screen on my dash/consol has flashed on an intermitant basis: "Service 4WD Switch".  It happened about two weeks ago and again last friday.  The first time was a single instance and friday it happened 4 times.  Nothing the past two days. I am unable to find any info about servicing this switch or where it is located.  I tried to buy a new one from a dealer and they said it had to be ordered and was a "vacuum switch".  Turns out they were looking at a 242 case (supposedly using my VIN).  I looked at my 249 case and couldn't see anything resembling the unit used on the 242.

Can you tell me where this switch is located and what to call it when ordering a replacement.  Also any servicing info you might know.
Thanks

Answer
There's a switch located on the driver's side of the case.  It's sort of on the top but between the front driveshaft and the main section of the case.  I've searched for about 20 mins on one or two sights and that's the only sensor I can find on the case aside from the speed sensor which is on the back side.

This switch if I'm not mistaken is alot like the range/PRNDL switch for the transmission.  It's got a ball bearing on the inside that moves in and out on a gear like component inside the case.  Each position of the 4x4 shifter corresponds to a different depth that the ball moves to on the gear like component.  The switch changes resistance sending back an indication as to what position the shifter is in.  Or... in your case what position the switch THINKS the shifter is in.  

The 4x4 is physically not changing gears so damage to the transmission/driveline isn't going to happen but obviously a change in the switch state WILL show a change in indication on the display module.  I do not know if this makes any change to powertrain control systems so you may want to continue on with your plans to replace the switch.
Doug