After having this problem and reading some of the info available I wne t about the following task. First and with much reluctance I went to the Ford dealer since the HAll sensors are a FORD only part. They have also gotten quite pricey.....$60.00 for the front and $70.00 for the rear. Now for those who dont want to throw money away on what is an expensive experiment....I say this because the dealer has no absolute fix for this......its a step by step repalcement of parts which can add up to quite a bill.
It is a simple known fact that the hall sensors fail.......sadly you cant tell which one and as one knows.....these are electrical items which are not returnable/refundable.
So.....let me tell you what I did......take a little excursion to your local salvage yard/u-pull it yard if a vailable. The entire shift motor and both sensors will unbolt and un-plug. A fairly simple removal that can be done under the vehicle. Swap out the entire assembly for yours....the only wire needed to splice will be the brown wire which goes into the tranfer case.
This solved my problem as it eliminated multiple possibilites....poor conduction in the motor and the guesswork of which sensor...front or back. Cost....about $20.00 and perhaps 30 minutes to do the swap.
two important things to note....if your getting the used part.....find a vehicle that was damaged in a collision so that it was probably running ok prior to its accident. This will usually solve about 90% of the time.....the other 10% involves a possible relay/electrical issues.
Dont let anyone sell you on a transfer case before doing a lot of checking........my blinking lights began some months after I installed a new
tranfer case and found that all the other exteral parts were swapped over.
Hope this helps
PS: my 97 Explorer has 196,600 miles and there is no reason to think it wont go another 100,000. They are great vehicles as long as properly maintained.