Its almost always the PNP switch has died and the cost of replacing is usually results in the car being scrapped.
I sold an amazing and freakishly powerful S70T5 auto to a freinds sister on mid north coast NSW and she loved it but when that switch went they had to scrap it.....
No point at ALL putting a used one in and new is probably the same cost as the car is worth.
The car is old, ive never heard of the interweb methods fixing it and its age is an indicator that it is stuffed so really, buy another car.
*Unless you can fix it yourself and can waste good money on a new part......