I don't know about the Jeep side of things, I'm an electronics engineer.
It is probably a Hall effect sensor. If it has 3 wires. Brown is + 12 Volts, Blue is Common, and the third wire would be the pulse output.
If you take that third wire and "with it disconnected" from the sensor, quickly make, and break it to ground, the speedometer should give a reading.
If the color of the wires is not what I think, see if you can find me a number from the sensor.
Also, if you post your jeep type/year, I am sure more people here can help.
Good luck...