Speedometer sensor
A small, cylindrical object with two spade connectors mounted in the transmission case (not to be confused with the reverse light switch). The speedo sensor can go bad and it makes speedometer operate intermittently, or not at all.
A number of Alfa Romeos have such electronic speed sensor unit, located at the beginning of the transmission (just after the clutch bellhousing on the driver side). GTV6, Milano (75), Alfetta 2.0, Giulietta 1.6, Alfa 90 .
The basic function of this sensor is to send impulses of current to the speedometer unit, thus they have an impulses/turn characteristic. I have seen two variations - 4 imp/turn and 6 imp/turn.
The sender has a generator inside (couple of transistors, resistors, capacitors), a sensing device (coil + metal-leg rotor or gerkon + n-pole magnet rotor). When rotor turns (by transmission gears) and its leg(pole) pass coil(gerkon) the generator excites, and sends an impulse of current via the wire. The sensor has two contacts, one is for 12V, the other leads to speedometer circuit.
NOTE - this sensor cost was about $75 US / last time I replaced it. units may differ for use in 85 MPH vs. 125 MPH speedometers in a later production GTV6
Tim Philip contacted me recently with advice on actually repairing the senders. See the Digest Clippings for details.
If a Milano (75) gearbox is installed in a GTV6, the Milano speedo sender must be retained. This can be made to work with the GTV6 equipment by using the amplifier from a Milano (installed under the rear seat) as well as a speedometer from a 1986 (or late '85) GTV6
