My tach works fine until I have been riding for a while and then starts spastically bouncing around above 3k rpm. I have checked and cleaned all grounds, did a quick check for worn wires, checked the pink wire from the ECM to the gauge cluster, done the wiggle test, etc. What is odd is that I am not getting any codes, the RPMs from logged rides are normal, no spastic bouncing in the log, and runs fine. Probably not a real issue but the tach needle is driving me crazy!

Narrowing it down to a worn wire or bad connection somewhere, which will take some time to check. Then today I got to wondering what input the ECM uses for the output to the tach. Maybe the issue isn't the output but the input (Garbage in garbage out). Does anyone know what input is used by the ECM for the tach output? I tried figuring it out from the wiring schematic but it is beyond limited electrician interpretation skills.