Where is the PNP sw located?

It is located inside the transmission as part of the control module and valve body. To test it you need to use a scan tool to verify if the switch is changing state from off to on when in park or neutral. Then you use a meter at the ECM on terminal 102 to verify that when the lever is in park or neutral that pin shows zero volts, if it is in other positions, it will show battery voltage. However, your description of an intermittent sounds more like a connection issue, for that I would go under the truck and disconnect the harness at the transmission, inspect it for corrosion or transmission fluid. Clean it and reconnect, does it start properly now? If not then do the above testing, the factory service manual basically says, test that wire for operation, use the scan tool and if it's still wrong, replace the valve body in the transmission. Then use the scan tool to program the new module so it will even function.

Hope it stays fixed. Pin fitment seems to be a problem more now than ever before.