Have you checked for the 26 pin green under rear seat?
May be you can ask them for a converting 12/26 harness, ...
the signals should be there.
Javier
Did you find the 26 pins green connector in your car? ...
Did you get from archives the pin out for the 26 pins?
http://www.bimmer.info/forum/attachm...tachmentid=997
To hook it in the trunk is worse than to hook it at the 26 pin, you can tap there to the wires just before the connector plug ending the harness, and get full operation of doors/hood/trunk lid monitoring for antitheft operation, besides keyless.
You may even send your provider a table with the 26 pin wires (you can even confirm in your car they are as said in the table), and get from the provider wiring instructions.
My concern would be if they need "to ground" or "to 12V" signals from the jamb and key switches. Also compatibility of actuating signals to the GM for keyless entry.
If they give you their harness pin out and operating ranges, we can help you with wiring instructions.
This is only justifiable if the investment in the system was low and alternatives ready to go are much more expensive, as you will tap into the wires and you may not get full operation of the system (I mean for example "Alarm may not be deactivated with keyless, or any key hole in the car").
Javier