Garage Cabinets, Garage Storage, and Garage Organization

I am fitting a Navigation and Telemetry system to a BMW740li, (2007 model) which is required to operate by the insertion of a special coded key, which when recognised enables the vehicle to be started.  It is a secondary security system in effect.  For this to be effective the starter circuit is normally cut and a pair of wires (from the security device) are then joined to these wires, which in turn are linked to a relay in the security device thus enabling the circuit to be made on insertion of the coded key.

On most vehiclest the starter circuit wiring is normally traced from the ignition barrel and a cut made somewhere along this wire.  As the system on the BMW does not have a 'normal' ignition barrel it is difficult to find an alternative.  I was going to see if it is possible to link into the the wire that goes to the brake pedal, as this must be depressed for the vehicle to start.  Does anyone know if this is possible or if there is an alternative position where I could make this cut?  Any ideas much appreciated.  :bow: