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Is that not the switch on the injection pump that controls the shifting of the transmission? If so it is on the drivers side of the injection pump and moves with the throttle lever.
OK, sounds kind of crazy...but in the past when I have gotten a code and had no idea where the faulty part was...but knew it was faulty, I would go ahead and buy the part then just look for it on the engine. Then go ahead and replace it. I know this sounds crude, but my '90 F-250 had so much spaghetti under the hood, it was difficult to track down some of the parts...especially the emissions related parts....without a book that many times I would just but the part then match it up...believe it or not it worked most of the time. :-X12
I believe the part you are looking for is on the drivers side of the injection pump mounted where the throttle shaft comes thru the pump housing. It rotates internally and acts like a switch, indicating the position of the throttle.