Surprisingly the new gearbox's speedometer cable connects to the Mini speedometer. Unfortunately it interferes with the body at the gearbox end so I haven't been able to test it's calibration. I've been using the speed display on my EVision which listens to a speed pulse from my motor controller, but there is no odometer or trip meter and I would like to use display other data on the EVision, so I've been looking for an electronic speedometer to mount inside the mini instrument cluster. At the weekend I found a small electronic speedo from a Mitsubishi FTO which was new enough to be electronic but old enough to not be use the CAN bus and be small and separate from the other gauges.
The speedometer input is pulled up to 5v and pulled down by a transistor in speed sensor in the gearbox. I made a simple Arduino sketch and found it requires 2548 pulses per km and very slightly over reads at 100km/h. Interestingly it works at 400km/h! The speedo needle almost touches the other side of the zero stop but the odometer works perfectly. I haven't tested to find the speed at which it stops working.
The mechanism is small enough to fit into the mini instrument pod, but the face is too big. The original mini face will fit if I make the window for the odometer bigger and enlarge the center hole slightly. The shaft is smaller but it shouldn't be too hard to fit the mini needle. I'm not sure if I should mount a remote trip meter button, or drill through everything and try to mount a button in the normal position. I'm now designing an adapter to mount the mechanism. Interestingly both cars have 180km/h speedometers, but the Mini spreads it out over more degrees. I'm not sure how hard it will be to calibrate the needle.
I'm considering whether to wind the speedo forward to 200,000km and call that "electric zero" or to attempt to align it with the car's current speedo -- TachoSoft indicate that the mileage data is stored in a separate serial EEPROM.