Are you past your 3 year warranty? This seems like something Royal Enfield would fix.
I thought it was a 2 year warranty? Regardless, I bought mine used from a private seller. It's a 2020 INT650. Not sure if the warranty still applies. I've also made some modifications to the lights on the bike and removed quite a bit of front end/rear end bulk which might void the warranty.
Anyway.... Last update - I fixed it! Put the new 'Himalayan' sensor on, still no dice. Opened up the headlight and disconnected, cleaned, greased, and reconnected every plug. Removed the front wheel and inspected everything (all looked good). Last ditch effort was to clip about an inch off the end of the original (broken) sensor wires and re-crimp some new box contacts. Put everything back together and I now have a perfectly working speedo.
Not sure which one of the above fixed it, but I really don't care as long as it's fixed. I'll be returning the Himalayan sensor and drive unit since I didn't end up using it.
I gotta be honest - I've worked on a lot of machines. The wiring loom on these bikes is pretty horrendous. I've never seen an OEM use cheap electrical tape to wrap an entire harness. Tape unwrapping itself, Lots of contact crimps are badly crimped/loose. Wires are too long or too short. Lots of kinking. Way too much thick white grease on everything. I love this bike, but I can see where they saved some $$ on skilled labor and materials.