Larry, as it regards the how do I make the jumper portion of your question....and I think @Jebiruph Jerry would agree with this because it just is what it is..How did you make your Jumper...please give me the specs or where you got it. How do you keep the Aux Battery charged, or will it charge with the Jumper in place. I know it's somewhere in the thread but I would like to know exactly what you are using...Thanks, Larry
by virtue of your 2019 ownership you neither need said jumper nor will it do you much good regarding its original intention...to get your 3.6L JL cold cranked if the ESS/Aux battery is dead.
A quick history lesson's required here. 2018 3.6L JLs that have not since been upgraded with a flash whose details I won't get into--because it doesn't apply to you, benefitted from Jerry's jumper because they would not crank if the ESS/Aux battery lacked adequate charge--even if the main battery had all the power in the world.
The upgraded 2018's (3.6L that is) and all model year (3.6L's) thereafter do not get stranded upon attempts to cold crank them if the ESS/Aux battery is dead. They automatically attempt, on second crank try, the main battery.
With factory or Jerry's original jumper in place the Aux battery is charged when the engine is cranked. I'm not a fan of using ESS with Jerry's jumper because with it in place, ESS events no longer solely tax the ESS battery as per factory design, instead tapping both batteries.
(Jerry's original jumper hard wired both batteries in parallel. By factory standards those batteries were always hardwired but for a second at cold crank and ESS events.)
It's probably me being too careful, but the whole idea of isolating the batteries during an ESS even,t so the main battery has enough power to bear the brunt of the load in cranking the engine does not happen with his jumper.
That is NOT a critique of Jerry's brilliance, just a contraindication for its use with IMHO, ESS.
Now, that said, and since Jerry's initial creation of that jumper, he has gone on to build upon that initial design and create ingenious mechanisms to allow the 3.6L JL to operate by factory, with just one (either) battery, or both batteries always connected (i.e. his jumper).
It's all great stuff, but bottom line, before you go rewiring, what best happens first is an assessment of your needs.
And if those needs are only "I need to know that if the ESS/Aux battery dies I can still crank the engine (on the second try,)" then you are "Dorothy and her desire to go home from Oz."
Your 2019 (assuming 3.6L) had that "power" all along. : - )