the white/gn wire is a vehicle speed signal. I do not know what the ECM uses that information for, but the TSM uses it to operate your self canceling turn signals.
if that wire is clipped, I have to wonder what other wiring nightmares you may be looking at.
your speedo system is very simple........the speed sensor connects to the speedometer, the speedometer is connected to 12v and ground (with a few extra wires for indications that have nothing to do with the speedo).
since you have replaced both of the usual suspects, a wiring problem is all that is left.
you will have to be patient. you need to start at the speedo and check every pin/socket on every electrical connector. you need top verify the pin/sockets are inserted fully in the connector and you will need to pull every wire and verify a proper connection where the pin/socket is crimped to the wire.
you should also check for pinched wires, splices, electrical tape, butt splices or any other sign the wiring has been tampered with or modified.
if I were you, I would purchase the HD service manual for the bike. the schematics are excellent and the electrical section contains a lot of information about the wiring connectors and the pins/sockets used.
I will help you all I can, but it would be a lot easier for you to actually see the pictures and read the instructions.
the main harness plugs into the speedo.
the speed sensor has a 3 pin connector between the sensor and the speedo connector.
let me know if you need more help.