Begin by removing your current MID/OBC. There is a hole in the roof of the storage pocket, stick your finger in there, feel for the back of the MID/OBC and push it out. You can use a dull butter knife to pry it out from the front whiles pushing from the back.
Remove lower kick panel (three star point screws),
Remove Knee Bolster (three 11mm bolts)
Remove the Odometer. In my car to do this I MUST REMOVE THE STEERING WHEEL. Most DIY say you do not and can simply squeeze the Odometer out behind the steering wheel. I can do that and trying means scratching the steering wheel and possibly breaking something I do not want to. Just unplug the battery and remove the air bag (two size 30 Torx head screws behind the wheel), then unplug the airbag, and remove the wheel bolt (marking it so you keep it aligned when you replace it)
, then slide the Odometer off and disconnect it's three connectors to release it from the dash.
Cut off your original 7 or 11 Button OBC Black Connector Harness from the wiring going into the car and get ready to spend the next few minutes splicing. As you can see the original 7 or 11 button MID/OBC harness has most of the wiring on it already so all you have to do is line up the wire colors (or pin slot #s if you marked them)
of the wires going into the car with the 18 Button Black Connecter and splice them with the Heat Shrinks. These are ;
Pin Slot-10 and 11 (White/Blue and White/Red); Provides Chime 1 and 2 for CHECK warning, Freezing Temperature, Alarm Warnings for CODE and Door Open w/ key in Ignition.
Pin Slot 12 (Brown/Grey2); Provides External Temperature data
Pin Slot 13 (Black/White); Odometer-Controls the Dimming Feature on OBC so it dims in conjunction with Odometer and dash lights.
Pin Slot 14 (Purple/White) ; Fuse F45- Powers the OBC
Pin Slot 15 (Blue/Purple/White); X17 Pin 24 (Odometer)
Pin Slot 16 (Grey/Red); X16 Pin 2 (Odometer) Powers Lights on OBC
Pin Slot 3, 4 and 5 (White/Green, White/Blue, White/Grey) If you had the 11 Button OBC then this will also be prewired to the Check Control Module so just splice them here. If you had the 7 Button MID/OBC, then these wires going into the car are not present.
Pin Slot 1 and 2 (Brown/Grey1 and Blue/Red) if you had the 11 Button OBC with Check Control then these are already prewired to the Brake Lights so just splice them here. If you had the 7 Button MID/OBC, then these wires going into the car are not present.
Now Splice the 18 Button White Connector to the remaining wiring going into the car that were on the old 7 or 11 Button MID/OBC’s Black Connector. These are;
Formally Pin Slot 17 on old Black Connector now Pin 8 on White Connector (Red/Yellow); This powers the 18 Button OBC.
Formally Pin Slot 18 on old Black Connector now Pin 13 on White Connector (Brown); This grounds the 18 Button OBC.
That is about 60% to 70% of all the wiring and 50% of the DIY. You are almost done and now its time to finish off splicing the remaining pigtails on the new White and Black Connectors of the 18 Button OBC.