My homie just swaped his sohc for a dohc and threw his OBDI manual tranny on a OBDII automatic motor and a accidently ordered a OBDI harness. Is there a way to splice the OBDI harness to make it fit the OBDII motor or should he just order a OBDII harness?????

 

Dude if he had the old sohc and he swapped to dohc he should just change out the ditributor and TB for OBD1. (eventually swap cams). ECU tuning for OBD1 is cheaper than OBD2 emulation.
But if he doesn't want to swap anything out he should just make everything OBD2.
You can splice it but it takes time and there are more room for errors, would be better if he just traded it in my opinion.