Let me ask my question another way. Can the pack be left in the car with breaker OFF and change the harness to add the arduino to test/drive the car? Wouldnt the 12v battery then still be charged and the other bcm and mcm become nothings to the system? Maybe upplug the battery plugs too? If this is possible, then the testing and use of the arduino could still be tested/used till the pack could be removed and bypassed. Does this sound doable?