What might cause a 1999 Toyota 4 Runner automatic to be locked in park?

It is true there's a mechanical lock on the transmission which requires the brake pedal to be depressed in order to shift out of park. However, a more simple explanation than below could be the result of a blown fuse for the brake lights found under the hood within the main fuse box. I encountered this problem when using a friends utility trailer. The brake/turning light wiring on the trailer wasn't properly grounded. I had it plugged into a 4 straight trailer wire harness. The first time I stepped on the brakes, there was an ungrounded surge sent to the brake lights, blowing the rear left bulb and then the fuse under the hood. If you encounter this problem in a pinch, the fuse for the rear window defrost is the same amp rating and is located in the same fuse box, but be sure to unplug the trailer before you blow another fuse. As a reminder, I didn't know anything was wrong until I finally stopped and parked the car, at which point I couldn't get it out of park. It was then I diagnosed the problem. The main reason is that the brake pedal must be depressed in order for the shifter to be operated from the Park position. There's a mechanical block that is released when the pedal is pushed. I believe that there's a release inside of the slot that the shift lever operates in. Off the top of my head, I recall that it's in the rearmost part of the slot (towards the back of the car) and a curled finger inserted into the slot, finding a little plastic bar and pulling it forward will release the lock so that you may operate the shifter without pressing the brake pedal. I found that if you take off the neg terminal of the battery that the shifter will not operate at all.