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Old 09-08-2021, 06:09 PM   #1
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Question about 12V charging while flat towing JL

I've flat towed a TJ and JK behind the MH with zero problems. Now I'm getting ready to flat tow my 2018 JL. It is a whole new beast as far as the electrical system goes with it infamous stop/start system and two batteries.

I'm using the Cooltech wiring harness and a Brake Buddy II braking system. I'll power the Brake Buddy from the 12V outlet in the back cargo area since it is live all the time.

So, here is the question. Do I need an axillary charging system to keep the battery up for the Brake Buddy on the JL? Cooltech is pushing their charger. Is it a real need or just revenue enhancement. On the TJ and JK I never worried about the Brake Buddy draining the battery on a one day tow. If I towed for two or more days, I would just let the engine idle for ten minutes or so first thing in the morning to top off the battery.
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Old 09-11-2021, 10:46 AM   #2
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Just to be clear, we are not "pushing" anything. We do have a package that includes the RVi charger - typically for those people who will tow with an aux braking system that relies on Jeep power. My opinion is that most aux braking systems are relatively passive - they brake when you do but then they're back off again and unless you are towing for long distance with a lot of brake applications, a charger may not be needed.

But, a question I DO have is if your JL has the OEM LED light package. If so, then there's a battery drain potential and if the moderators would allow, I can elaborate more about both the problem as well as a solution.
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Old 09-11-2021, 09:07 PM   #3
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Given the complexity of today’s new cars electrical systems, I don’t think I’d go down the road without a battery tender/charger. It’s certainly not going to hurt anything, and sometimes a discharged battery will wreak havoc on a car. I’m also not sure 10 minutes at idle is really enough to charge a battery unless it’s not discharged by very much. IMHO, it’s cheap insurance.
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Old 09-11-2021, 09:23 PM   #4
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Quote:
Originally Posted by CoolTech View Post
Just to be clear, we are not "pushing" anything. We do have a package that includes the RVi charger - typically for those people who will tow with an aux braking system that relies on Jeep power. My opinion is that most aux braking systems are relatively passive - they brake when you do but then they're back off again and unless you are towing for long distance with a lot of brake applications, a charger may not be needed.



But, a question I DO have is if your JL has the OEM LED light package. If so, then there's a battery drain potential and if the moderators would allow, I can elaborate more about both the problem as well as a solution.
I have the cooltech kit, oem led light, and rvi charger. I would like to know more about the potential drain and solution.
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Old 09-13-2021, 11:55 AM   #5
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Quote:
Originally Posted by CoolTech View Post
Just to be clear, we are not "pushing" anything. We do have a package that includes the RVi charger - typically for those people who will tow with an aux braking system that relies on Jeep power. My opinion is that most aux braking systems are relatively passive - they brake when you do but then they're back off again and unless you are towing for long distance with a lot of brake applications, a charger may not be needed.

But, a question I DO have is if your JL has the OEM LED light package. If so, then there's a battery drain potential and if the moderators would allow, I can elaborate more about both the problem as well as a solution.
I am curious about the battery drain potential as I am in the process of setting up our 2020 JL Rubicon (w/oem LED) for flat towing. I know it doesn't take much to kill our Jeep batteries (12V and 6V aux)...already have had to charge the batteries 2X.
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Old 09-14-2021, 05:02 AM   #6
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I am curious about the battery drain potential as I am in the process of setting up our 2020 JL Rubicon (w/oem LED) for flat towing. I know it doesn't take much to kill our Jeep batteries (12V and 6V aux)...already have had to charge the batteries 2X.
Cooltech, please elaborate on this subject as my JL has the OEM/LED lighting package.
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Old 09-14-2021, 08:19 AM   #7
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To summarize and be as specific as possible, the problem occurs because on LED equipped Jeeps, there is an extra wire in the harness. The purpose of this wire is to inform the Body Control Module (BCM) that the OEM LED light is functioning. Traditional (non-OEM) bulbs don't need this wire because if a filament breaks, a simple continuity test can tell the BCM if a bulb is functioning.

When an aftermarket tow harness is installed in one of these 2018+ Wrangler/Gladiator and the rear light (either parking, turn/brake) is activated, this additional wire causes the BCM to wake-up the Jeep from a sleep-state. Each light activation will cause the Jeep to wake-up and it will consume a minimum of 3-6 amps in this awake-state.

This occurs by virtue of illuminating one of the rear lights. ALL tow harnesses - even the OEM MOPAR harness will experience this problem.

MANY people may believe they don't have the problem - but it is because they are towing in the daylight and do not have a lot of rear light activations. In these conditions - and shorter tow times - maybe 3-4 hours, the charge in the Jeep battery may not be depleted to a level where the Jeep cannot start.
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Old 09-14-2021, 08:24 AM   #8
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They are not very active on the RV page, but they have a lot of information posted on the Jeep forums.



The executive summary of the problem relates to the way the original cooltech wiring harness (and all others too) makes the connection to the rear lights.


In a standard fillament, the jeep's ECM can detect a bulb out based on a broken circuit. This is not as easy with a DIODE, and requires another circuit just for this test.


The additional circuit provides feedback for the electrical connection. This feedback is waking up the jeeps computer from its deep sleep, since this wire was not disconnected during the cooltech switch setup. Everytime you use your brakes or turn signal, it wakes up the computer for a few minutes and continues to draw power.


Driving for long distances at night or in the rain with the lights on will have the effect of keeping the jeeps computer on the entire time.


I have the RVI charger to keep the battery topped off, but had a few times when the main battery was dead. I use a brake buddy, and thought that maybe the brake buddy was set too sensitive. Now that I understand what happened, it makes more sense that the ECM drained the battery.


Even with the RVI charger in place, long distance driving for multiple days with lights on will drain the jeep battery.


MY*JLUR is a 3.6L without the e-torque. I have 2 batteries, one small one under the primary dedicated to a stop start feature. Since I don't use the stop start feature, I have rewired this battery to be a cold-spare. I fully charge it, and then take it off line with a toggle switch. This saved my bacon when I had the dead battery after the tow, as I just had to flip the switch, and start the jeep.


If you don't have this option for you, at least carry a good set of jumper cables and understand the proper way to jump start a JL. It is not as simple as plug up the batteries, as you have to bypass the start stop battery and use a jumper.


Lots of discussion on the JL forums about this.
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Old 09-14-2021, 09:26 AM   #9
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Is this for any vehicle with LED lighting or just Mopars?
Wouldn't simply installing diodes at the tail lights solve this issue?
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Old 09-14-2021, 10:04 AM   #10
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Is this for any vehicle with LED lighting or just Mopars?
Wouldn't simply installing diodes at the tail lights solve this issue?

It is a problem with Jeep Wrangler and Jeep Cheerokee for certain.


All vehicles are now mandated by the EPA to show a message on the dash when a bulb is out. This is not possible using traditional methods when an LED is used.


A diode will not solve it as there is a 3rd wire providing this feedback.


How the ECM responds to this signal is where the true issue is. When the ECM knows the vehicle is not running, there is no reason for it to respond to this signal. Especially in a vehicle that is designed and known for being flat towed. This is where the problem comes from.


Cooltechs solution requires another switch installed alongside the already existing switch. For me, the battery bypass mod works much better, and I don't want to add another switch.
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Old 09-14-2021, 10:54 AM   #11
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Is this for any vehicle with LED lighting or just Mopars?
Wouldn't simply installing diodes at the tail lights solve this issue?
Unfortunately, no. The function of a diode is to prevent current from flowing in a direction that is not desired. When the Jeep is running, it is important that it "sees" feedback on this wire. When it is being towed, you DON'T want any feedback on this wire - because the feedback signal causes the BCM to wake up the Jeep.
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Old 09-14-2021, 12:04 PM   #12
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Unfortunately, no. The function of a diode is to prevent current from flowing in a direction that is not desired. When the Jeep is running, it is important that it "sees" feedback on this wire. When it is being towed, you DON'T want any feedback on this wire - because the feedback signal causes the BCM to wake up the Jeep.
A couple of toggle switches wired as a by-pass would solve that but the operator would need to remember to open them when towing the LED equipped vehicle.
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Old 09-14-2021, 12:27 PM   #13
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A couple of toggle switches wired as a by-pass would solve that but the operator would need to remember to open them when towing the LED equipped vehicle.
That is the solution provided by cooltech on their website.
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Old 09-14-2021, 12:47 PM   #14
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To summarize and be as specific as possible, the problem occurs because on LED equipped Jeeps, there is an extra wire in the harness. The purpose of this wire is to inform the Body Control Module (BCM) that the OEM LED light is functioning. Traditional (non-OEM) bulbs don't need this wire because if a filament breaks, a simple continuity test can tell the BCM if a bulb is functioning.

When an aftermarket tow harness is installed in one of these 2018+ Wrangler/Gladiator and the rear light (either parking, turn/brake) is activated, this additional wire causes the BCM to wake-up the Jeep from a sleep-state. Each light activation will cause the Jeep to wake-up and it will consume a minimum of 3-6 amps in this awake-state.

This occurs by virtue of illuminating one of the rear lights. ALL tow harnesses - even the OEM MOPAR harness will experience this problem.

MANY people may believe they don't have the problem - but it is because they are towing in the daylight and do not have a lot of rear light activations. In these conditions - and shorter tow times - maybe 3-4 hours, the charge in the Jeep battery may not be depleted to a level where the Jeep cannot start.
Thank you for this information. This will no doubt show up on future Internet searches. Now I understand the issue.
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