How do I set the "Liftgate" sensor?

[Pinko]

I bought my Grand Cherokee about 3 weeks ago (2000 model) and this weekend it started displaying on the central computer that the lifgate is open every time I go over a bad patch of road.

Driving along, it would beep, the lights turn on, the "Liftgate Open" message appears and then a little further on down the road, the message dissapears and the lights go off. This happens in regular intervals - very frustrating.

Someone on the message board suggested that it may be the sensor for the liftgate that needs to be set. Would anyone be able to tell me how to do that please?

Thanks!