2001 Mercury Villager shift linkage

First thing to check are the brake light, do they work? If not, there are two switches (sometimes one) on the brake pedal arm, top one is for the shiftlock actuator, bottom one is for the brake lights. Both must work for the shift lock to work.

Usually it turns out to be a faulty wire, they tend to break where they bend, unplug the wires, use an ohm meter at the switch with pedal pressed it should have 0 ohms, released it should be infinite. Then look at the wires, you may find cracked insulatiion or a bad connection at the end. You might need a sharp probe to pierce the insulation at sevaral pionts and the other lead remains at the connector end, when meter reads OL you have a break!