I hope a mechanic did not tell your friend that the trans had to be dropped to make the repair. If that is the case, they need to run and never go back.

The switch is called a PNP switch, it senses the gear that is selected, controls the starter to prevent starting while in a gear other that park, and also activates the reverse lights. Below is the link to change it.

The switch itself can be repaired and reinstalled. What causes the problem is the closeness to the exhaust down pipe, it gets hot with use, cooks the grease inside the switch and prevents the electrical contacts from doing their job. Take it apart, clean the surfaces with a degreaser, careful of the small springs, re grease with a good quality synthetic grease and reassemble. Very easy to do.


http://www.brickboard.com/FAQ/700-900/TransmissionAutoAW30.htm#960AW3040GearPositionSensorSwitchReplacement

DanR '94 964 342,000 miles (108,000 on the new engine)
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DanR