Just rewire the OBDII male connector from the OBDIIc&c gage so the 12 volt supply comes from the car switched 12 volt bus. No relays, no timer etc.Could there not be a relay (or a circuit) which simply turns it off when the ignition is off (or to be really clever, when the ignition has been off for a chosen time-period?) This would avoid the 'parked at the airport' problem for those of us too absent-minded to unplug the connector. Basically, unplugging every time one parks up is uncomfortable, and eventually not a very good way to treat a multi-pin connector.
Best regards, Tony.
On my website I show how I modified the OBDII connector with a socket to allow this to be done. This mod does not involve changing the car OBDII connector wiring at all. It's a small 2 pin jack and socket similar to a mono earphone plug/socket.
I picked up the switched 12 volts from the DRL fuse under the dash.
Pete: Another item to [hopefully] add to the list of fixes.
Have the display back light brightness setting to be saved so it doesn't have to be reset if the 12 volts is removed from the gage.