I have and obd2 to obd1 conversion harness to an p72 ecu in my 97 gsr-t. I want to hook a pin to b6 or d12 for an analog input to my neptune rtp. Is there an unused pin like secondary 02 that I can just pull out, cut and place into b6 and splice into my input device? I know I can buy them and go to a junk yard but this would save me a trip.

 

Yep! Secodary O2 sensor wires are a perfect choice. They're not being looked at by the obd1 ecu and it's already ran in the harness.
I don't have the pin assignment in front of me unfortunately.
You could Also use the power steering pressure switch if you don't have PS. And the AC input as well If you don't have AC.

 

I see d13 as the secondary 02 sensor ground and d14 as the Secondary 02. I don't see a ground for the primary 02. I know I can use d14 but do you think d13 is a possibility down the road or is it shared with the primary or something else? I use the ac switch for two boost maps and I still have power steering with 500hp I also have cruise control for long beach trips and using eld for boost control.

 

Sweet setup!
Sorry, I don't have wiring diagrams for that either in front of me. But an easy way to check could be to unpin it and verify all your other inputs and ouputs are still functional.
If everything's still happy, I would think it would be ok to use.