Tachometer and Speedo Not Working

[Big T 0]

I was having trouble with the heat sensor and inspected all wiring for the heat sensor, knock sensor and oil pressure sensor.  Al fine. Cut the green blue wire and ran a replacement and the heat sensor works.  However, next time I took the bike out the tachometer was wavering erratically and the speedo didn’t work. The tacho is now dead completely. I have normal voltage on the yellow/ geeen wire and continuity from the ECU. Ran an alternative cable from the speed sensor to the clocks but still no revs.  All connections seem fine. I’ve fiddle about with them all while the engine is running and not a twitch.  I’m completely stumped!  Any ideas?  Thanks.

[fast_eddy 712]

Check the earth wire to the frame for oxidisation.