Toyota Supra 2.5l Twin Turbo (JZA70) Digital Dashboard km/h to MPH Legend Conversion

The problem

All of the Digital dashboards fitted to MkIII supras are set to measure speed and distance in km/h and km.

By fitting a DSC Conversion unit from TRL Performance you can convert the necessary speed signals from the speed sensor to MPH, but this does not take care of the legends on the display which will still read km/h and km.

The solution

After dismantling fully the main dashboard unit, you are left with the main circuit boards. We are interested in the main central circuit board that houses the speedometer display. It is actually in two sections, and can be opened up to reveal the back of the display unit.
 

The main fluorescent panel has connections along both of the long edges. These connections transmit the signals from the display driver chips beneath it to light the individual segments on the display.

To convert the dashboard to mph from km/h all you need to do is locate the pins that supply power to all four segments (mph, km/h, miles and km)

To do the conversion you first need to remove the supply of power to pins 21 and 51 which will cause the km/h and km legends to go out. I found the best way to do this was to get a fine pair of cutters and physically remove the pin going from the board to the display, but please note, this is now the point of no return. You are physically cutting the feeds to these legends and it would be pretty difficult to wire these back in without damaging the display.

The power that was supplying these two pins is still present on the underside of the PCB, and you can use this to feed the power across to the appropriate pins that supply the MPH and MILES legends. Therefore you need to connect a small wire going from pins 138 to 21, and another wire going from pins 51 to 53.

Although not pictured, connecting pins 51 to 53 is very easy as they are quite close together. Below is what the dash looks like now that the legends have been converted.

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