Yep, that's what it is. It's very nicely done. Inside there is a reed relay which makes momentary contact as the magnet goes past. How do the wires look as they exit the "bolt". They are a bit vulnerable there. Can you check you are getting a pulse with a multimeter, or another way, is there a "time moving" counter in your speedo. If that's not going either, it points toward the pickup, or associated wiring. If the "time moving" counter is working, that would suggest the pickup and wiring is OK, and that there is problem within the speedo unit.