I recently solved a confusing electrical issue that i would like to share:

My '87 240 (wagon) has wires that run through the hinges to the rear door. These include brake lights, liscense plate lights, w/wiper, demist, and power locks.

When the car would not shut off with my foot on the brakes, and the rear demist light came on when a foot was on the brakes, i was stumped. Along with the engine running, all of the key-on things worked (stereo, guages, fan, etc...).

When you realize that power is getting from the always-on side (brakes always work), into the key-on side (rear demist), the problem is simple. In my case, the wires in the hinges were a mess, and the brake and demist wires were touching each-other.

Remember that:

-Power coming from inactive parts of the key switch is not always a bad key switch.
-The hinges on my 240 (probably many other cars too) can create major, and confusing problems, and are solved in a few hours of work putting in a new harness through the hinges.