The harness can be used, you just need to sort out few extras. 78F had the starter wired through clutch switch and neutral switch - for 71 you can remove that whole nonsense. The harness ground for 78F is at ignition coils while early Ks had it at seat lock. Also late bikes used front turn signals for running lights and have Left and Right turn signal indicator.
In my project I have the 78 harness and engine in K3 frame; I removed all the wrapping from the harness and sorted it out wire by wire and adopted it to my needs - like removing the safety starter module. Not hard to do and worth it, IMHO. The running lights I removed from the turn signal switch since it was not needed and wired turn signal indicator to the early K dash I am using.
