If the aux is connected, and the negative cable from the main touches ground of the jeep, it can short the N3, because the negative is still connected to the aux. it’s confusing, but anytime working on the jeep both the negative cables need to be separated and care must be taken to ensure nothing shorts out.
My main and aux battery were replaced about 3 1/2 years ago. I had the aux battery die on me at a stop light with the start/stop system engaged, locked my front & rear up and cost me about $700 at the time.
