I have a 2003 jeep grand Cherokee Lerado with select track, and the part time 4wd light on the dash stays on. when I put it in part time 4wd it goes out.

SOURCE: 2000 Jeep Gr. Cherokee 4WD 4.7L under dash fuse diagram

If you still have the pop off cover for the fuse box the amperage and position (number) along with the purpose served by each fuse is stamped on that cover.

SOURCE: engine code 95 jeep grand cherokee lerado

12 is a battery disconnect within the last 50 start cycles and 55 means the end of the diagnostic cycle.  Basically the computer found nothing wrong. The 12 code may seem incorrect if you haven't disconnected the battery recently, but from my experience the 12 code shows up almost all the time regardless.

SOURCE: 2005 Jeep Grand Cherokee (HEMI) Service Electric Brake System

Problem is a faulty Steering Angle Sensor (part of Steering Module) located in steering column ...replacement part $600.00.

SOURCE: 99 Jeep Grand Cherokee Brake light problem

You can adjust the switch by putting your thumbs on either side of the switch plunger and pushing toward the brake lever. The switch shaft will ratchet into the new position which is will then be depressed by the brake lever when it is the brake is not being depressed.

SOURCE: 2005 Jeep Liberty stuck in Part Time 4wd

I questioned the dealer about my 2005 because mine was disengaging what I thought to be rough compared to what I was used to. They told me that I should shift the vehicle into Neutral before shifting the selector. I have also found that shifting between Reverse and Drive a couple of times while stopped has helped as well. By doing these couple of things, I have had no trouble since. I hope this helps as it might at least be something to try.