From what you are describing, i had a similar issue which was resolved with help of the foum (thanks again guys). I bought an x5 tapped in rear, and active restraining system went active.. While not a single airbag deployed, system kicked the positive wire out of terminal and before issue was resolved, if I would attempt to start the car, all ligts would go on/off as normal, there would be a relay click under the hood but nothing else. So may be you should too check the "+" wire (the finger thick one)that goes off the battery and perhaps concider that problem you are having not a mechanical i. e. battery/starter/alternator but electrical key/ignition switch/key chip reader/theft preventing module and jave that diagnosed.

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2009 Range Rover Sport SC HST Limited Edition
2014 Infiniti Q50 AWD