[imack]

One possibility would be the wires that run into the rear hatch. They take a lot of stress with the open-close cycle of the hatch. You'd think they might use more flexible wire for this, but it's the same stuff they use everywhere in the car.

I had a problem on my '91 Escort wagon where the "door open" warning light would come on intermittently. After playing with the latch mechanism for a 2-3 hours, I noticed by accident that the light changed state as I was moving the hatch up and down. I opened up the rubber "grommet" that runs between the body and the hatch and found the broken wire.