How to install neutral safety switch on 1997 Chevy Blazer? (on transmission)

Installed switch on transmission but isn't adjusted properly or something. Does the shifter shaft (where the shift linkage bolts to) on the transmission need to be in the PARK or NEUTRAL position when I slide the switch on? I've tried both. In the PARK position, I can crank the engine and shift out of gear until I shift back into PARK, and then it locks up and won't let me shift without climbing underneath and manually shifting the linkage back into PARK. In NEUTRAL position, the engine will crank but won't let me shift out of gear at all. Brake lights work. What am I doing wrong? Btw, just had the tranny rebuilt. Neutral safety switch is brand new. Please guide me through this!