I am very interested to know the voltage and amps ratings of your 36V to 72V switch.
Also tapping the main battery pack for 12V is a bad ideea and can have only 2 outcomes :
1. The best case scenario: A lower range.
2. Destroying the tapped battery.
I understand your desire to be back on the road with your new toy, but taking bad shortcuts will only get you to more repairs, down time, and expenses.
The reason for those advice with no explanation you got is because those topics are old and all ready covered many times in the past, so don't take it personally. When you keep disregarding those basic rules, peoples will stop trying to help you.
Please try to stop your enthusiasm just for a moment and get more informations first.