Park safety switch wiring on 78 K15

I have purple and purple/white in my park safety switch plug. My 78 wiring manual says this should be circuit 5 with a yellow wire. Perhaps it was switched. But anyhow, I'm not sure which of the two wires needs to be tapped for the wire from ECM B10.

Thanks.

Not sure but if you have a multi-meter with the sharp tips you could stick and see which wire grounds when in park or neutral.