Tail Sensor defective?

My Tail light illuminates when my revs get up to 8000rpm.
I checked the manual which says it’s defective if I measure less than 5V between 2 specific wires. I measure 12v…
I have replaced the sensor now with a used one from a parts recycler because this part is obsolete, but I still get the same result.

Is the sensor defective if I read 12v? Should I be performing some other type of test or just live with this?