Odometer redundancy (ECM capture)

[Teller.John at orbital.com]

The electronic instrument panel in my 85 Buick stores the odometer mileage
in a small removable module that attaches to the back of the panel via a
.100 center dual row connector - a standard PC-type connector.  If the
instrument panel dies, this module gets transferred to the new panel.  The
panel works fine without the serial EEPROM (that's what I assume it is)
installed, but it spells out the word Error where the mileage count
normally goes.