Today I disconnected the harness from the ECU and tested the knock sensor resistance- 0.555 mega Ohms. Then disconnected the KS harness and tested that. 0.555 mega Ohms. Called Specialty Z and asked if that meant I was in the clear... Nope.
He's thinking somewhere along that 27 year old wire is an intermittent ground/short. So he's still saying to run a new wire to the ECU.