3.6L ESS Aux Battery Bypass

[AnebuR]

It definitely works.
I have had my "avengers" light on for a while and the negative disconnected from AUX battery.
Jeep starts right up.

What would happen if I left the negative connected?

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[correfe]

What would happen if I left the negative connected?

It can drain your main battery, which in turn can damage it and make to weak to start and maintain the jeep running.
At least that's what happened with me.
I replaced the main battery with an aftermarket, and left the bad AUX battery negative disconnected.

The first time you try to start with the AUX disconnected, it will not start and dash goes dark. Once it does that try again and it should start right up, and on the first try all other times.- this also confirms the software update that allows you to use main battery only.

 

[correfe]

What would happen if I left the negative connected?

BTW, @Jebiruph has found another solution to this.
see attached link.

https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/

 

[AnebuR]

BTW, @Jebiruph has found another solution to this.
see attached link.

https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/

Thanks. I've actually been testing that solution for over a week now, after chatting with Bill (Rhinebeck01) about it. Can confirm that it works perfectly and reliably without any issues. Definitely the way to go. If the aux battery isn't completely shot, one can keep it topped off with a charger and then use it for emergency starts if the main battery gets drained. Just pop the fuse back in, connect its negative cable back and press start.

 

[Chocolate Thunder]

I have what I hope will be a simple question with a simple answer. When removing the AUX battery from the system by disconnecting and insulating the negative cable at the main battery, which cable is the one to the AUX? I’m hoping someone knows do that I can do it in the dark without having to try to trace it.

3.6L non etorque 8 speed.

 

[Leisure Freak]

It's been a while since studying the thread but I recall the AUX is the cable that is slightly smaller in diameter. Hard for me to tell from your photo. Mine when looking at them there is a difference, the smaller being the one closest to the passenger side fender.

 

[Rhinebeck01]

I have what I hope will be a simple question with a simple answer. When removing the AUX battery from the system by disconnecting and insulating the negative cable at the main battery, which cable is the one to the AUX? I’m hoping someone knows do that I can do it in the dark without having to try to trace it.

3.6L non etorque 8 speed.

@Chocolate Thunder

Smaller diameter cable is the Aux negative.

Position of the Aux negative on the Main batteries, Neg terminal is dependent on the model year of the JL..... .... the Aux, Neg, is always the smaller diameter cable, regardless of model year.

 

[Chocolate Thunder]

They look about the same size in the dark. I’ll wait until I have enough light to trace it. Thanks.

 

[Soul Man]

You can't trace it. There is about 6" of exposed cable then they both get wrapped together in a loom.
My Aux was closest to passenger fender (2020).
You can feel the difference in the dark, even in the light almost easier to feel than see the difference, but it IS noticeable.

 

[BadA$$Rubi]

You can't trace it. There is about 6" of exposed cable then they both get wrapped together in a loom.
My Aux was closest to passenger fender (2020).
You can feel the difference in the dark, even in the light almost easier to feel than see the difference, but it IS noticeable.

Edit: Disconnect both the negative cables from the main battery negative terminal. Separate both negatives. Use a DC volt meter: Red lead on N1 terminal at High Current Fuse terminal strip. Black lead to each of the disconnected negative cables from the main battery. A voltage reading on one of the negative cables will indicate you have the corresponding aux. negative cable. This will be the one you want to tape off and leave disconnected. Pull the F42 fuse.

 

[JL18]

I have what I hope will be a simple question with a simple answer. When removing the AUX battery from the system by disconnecting and insulating the negative cable at the main battery, which cable is the one to the AUX? I’m hoping someone knows do that I can do it in the dark without having to try to trace it.

3.6L non etorque 8 speed.

On mine it’s the one on the left. The connector under your new winch ground cable

 

[SteadyC]

I have what I hope will be a simple question with a simple answer. When removing the AUX battery from the system by disconnecting and insulating the negative cable at the main battery, which cable is the one to the AUX? I’m hoping someone knows do that I can do it in the dark without having to try to trace it.

3.6L non etorque 8 speed.

With 2019, here’s your aux negative #6 , like my 2018, I saved this picture from rhine
https://www.jlwranglerforums.com/fo...aux-battery-bypass.17293/page-36#post-1810514

 

[Jebiruph]

I added a reference to the jumperless aux battery bypass post to the first post in this thread.
https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/

 

[Pahrump Geprge]

I've seen quite a few posts related to failed Aux batteries causing flaky or dead electronics, stalling and failing to start/auto restart. I've come up with a simple way to temporarily bypass a bad Aux battery (also blown PCR fuse or bad PCR) and get back on the road. Warning - this post contains a lot of informed assumptions, so post your related experiences to help validate or invalidate any information I've provided.

10/18/2022 Update - Here's a newer post with updated information describing how to bypass the aux battery without using a jumper.
https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/


Here's a picture of my bypass kit. The jumper is used to connect the N1 terminal to the N2 terminal. I wanted to be able to install the jumper securely, but still be able to quickly disconnect it. A fused jumper seemed to be the best and cheapest way to go. Removing the fuse is a simple way to disconnect the jumper and it protects against overloading the wire. I don't know how much current will pass through the wire, so I used the largest I could find.

6/26/2021 Update - Many have reported that the 30A fused jumper shown in this picture has not been adequate for their JL. Use the highest capacity fused jumper you can find and make sure the fuse is not rated too high for the wire, otherwise the wire will melt before the fuse blows.

Here's how I tested the bypass. I disconnected the Aux battery at N1 and the ground wire at the Main battery negative terminal to simulate a bad aux battery. The voltmeter confirms the disconnect with low voltage at N1.

Here's a shot of the dead instrument panel due to the disconnected Aux battery.

Here's the jumper installed between N1 and N2, voltmeter shows the Main battery voltage at N1.

Here's the live instrument panel.

Here's the instrument panel after starting, only error indicated is open hood.

For those interested, following are some diagrams to illustrate how I understand it works. (See this thread for additional information on the dual battery system https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/)

Here's the battery voltages on a working system, the PCR is connecting the batteries in parallel, both batteries providing power to everything. Normal operation is verified with 0 volts between N1 and N2.

Here's the effect of a failed Aux battery, no power to critical electronics. This should be verifiable by a voltage difference between N1 and N2.

Bypassing is accomplished by jumping N1 to N2. This diagram illustrates the jumper getting power back to the critical electronics.

(updated 04/13/2019)
Additional 3.6L ESS system information is available here.
3.6L ESS Dual Battery Consolidated Information
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

This post was very helpful. I permanently installed the jumper cable as shown, but removed the fuse.

 

[Rhinebeck01]

This post was very helpful. I permanently installed the jumper cable as shown, but removed the fuse.

@Pahrump Geprge

Huh........ please explain. Why .... because if you use a jumper, you do not need to pull F42 fuse.

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