Cleaning up some wiring. I don’t believe I ever had this connected. Should I?

3 wires in the harness 2 are connected. This one is not. 1979 Jaguar XJ6 series 2 with fuel injection.

 

there are 2 ignition systems for the S2 efi,...the white/slate/blue wire you refer to is for a standard system, the wire goes to tacho from ignition coil, if your tacho is working then someone has made an alternative fitting... i have complete schematics for early models> https://www.jaguar-wiring-schematics.info/index.htm