JLUR battery flatlining when flat towing

[Oakmanr]

I bypassed the entire Jeep system so it doesn't wake up the Jeep. I ran a lead from the positive battery terminal through a fuse to the auxiliary switch that I mounted on the brake pedal arm. It draws the power for the LED 3rd brake light right off the battery so it has no effect on the Jeep's system. This is the switch kit that I used for the 3rd brake light, then I tied in the lead running to the umbilical cord for the LED on the motorhome dash. https://www.etrailer.com/Tow-Bar-Braking-Systems/Roadmaster/RM-751490.html

I understand, I already have the mopar flat tow wiring harness installed, so I’m not interested in changing it out. Thanks for the input

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[CoolTech]

I bypassed the entire Jeep system so it doesn't wake up the Jeep.

If you have the optional rear LED lights on your Jeep, then you absolutely have the "wake-up" problem and your Jeep's battery will be drained on longer trips. If your JL does not have the OEM LED rear lights, you are good.

 

[CoolTech]

If you have the optional rear LED lights on your Jeep, then you absolutely have the "wake-up" problem and your Jeep's battery will be drained on longer trips. If your JL does not have the OEM LED rear lights, you are good.

Let me try to (briefly) explain. When your Jeep has rear LED lights, the wire that traditionally goes to a rear bulb instead goes to a circuit board. The LED light is mounted to this circuit board. But also on this circuit board is a fault-sense wire that goes back to the Body Control Module (BCM). The whole purpose of the circuit board and this fault sense wire is to let the BCM know that the LED light is functioning. An unfortunate consequence of this "reporting" is that when a tow harness.... like the CURT harness, the MOPAR Harness, the Cool Tech Harness, etc. energizes one of the wires for the rear lights, this fault-sense wire carries a signal back to the BCM and wakes up the Jeep.

 

[millsj]

I have been reading this tread with great interest. I have a 2021 Wrangler with the LED lights that we flat tow. I have the Air Force One braking system with the Cooltech wiring harness. I have twice had the dead battery issue after multi-day tows and what a PITA that is! I was going to install a charger until I ran across this thread, but will now be ordering the Cooltech fix.

At some point when testing the braking system/lights on the TOAD, I realized that the infotainment screen, instrument cluster screen and the shifter light illuminated when the RV brakes were applied. From reading this thread, I assume this is the Jeep "waking up".

After the second dead battery incident on our most recent trip, I found that disconnecting the negative battery cable prevented the screens in Jeep from lighting up. I did not completely separate the two negative battery cables, so the second smaller battery was still connected to ground. I only physically removed the negative battery connection from the large battery.

I didn't have any battery issues for the rest of the trip, but it also may have been because I didn't have any long enough tows to kill the battery.

I'm curious if my work around of disconnecting the battery really worked and if so, it is a very quick and easy way to prevent the dead battery. Takes about 30 seconds when connecting and disconnecting the Jeep.

Thanks again for coming up with a real fix for this issue!!

 

[ROK HEMI]

I tow my JLU behind my class A motorhome as well. I use the RVi3 brake controller. It requires a lot of power, more than a cigarette lighter socket is capable of. I did not want to install anything permanently so I run a clip on battery cable with a cigarette lighter socket on it directly from the battery to the brake controller. I also use wireless brake lights that I put on the back of the jeep. I do not turn the vehicle on at all, and the battery seems to last quite a long time.

 

[RubiBlueJLU]

Let me try to (briefly) explain. When your Jeep has rear LED lights, the wire that traditionally goes to a rear bulb instead goes to a circuit board. The LED light is mounted to this circuit board. But also on this circuit board is a fault-sense wire that goes back to the Body Control Module (BCM). The whole purpose of the circuit board and this fault sense wire is to let the BCM know that the LED light is functioning. An unfortunate consequence of this "reporting" is that when a tow harness.... like the CURT harness, the MOPAR Harness, the Cool Tech Harness, etc. energizes one of the wires for the rear lights, this fault-sense wire carries a signal back to the BCM and wakes up the Jeep.

Several fixes:
Splicing in a switch to disconnect "that" wire. Several harnesses now include that.
Adding in a charging wire. Band-aid fix, masks THE issue. Good add for powered barking systems.
Batter cable removal. Again, band-aid fix. Works, but takes work every time.
Above post describing added in relays. Great fix, a bit of work. Cool!

I run the Curt harness. Goes front to rear, no splice, plug and play. I chose to disconnect the sensor wire at the tail lights. One time, reversible fix that solves the dead battery syndrome.
2-1/2 years, 2600 miles of toads. Several multi-day and at night/rain tows. NEVER a dead battery on arrival.

There is a post about this disconnect, somewhere in here, with pictures. I can't find it at the moment.

Mike

 

[RubiBlueJLU]

Ah, found it. Post #211 in this thread. Page 15?

 

[millsj]

Several fixes:
I chose to disconnect the sensor wire at the tail lights. One time, reversible fix that solves the dead battery syndrome.
2-1/2 years, 2600 miles of toads. Several multi-day and at night/rain tows. NEVER a dead battery on arrival.

There is a post about this disconnect, somewhere in here, with pictures. I can't find it at the moment.

Mike

I remember reading about the sensor wire disconnect and need to go back and look for it. I have ordered the Cooltech fix so I won't have a problem moving forward. I installed the Cooltech light wiring harness, so I know exactly what I am getting into for the fix install.

Disconnecting the battery was a little bit of a pain, but much easier than dealing with a dead battery.

I'm really just curious if my battery disconnect band-aid "fix" is really a fix.

 

[millsj]

Ah, found it. Post #211 in this thread. Page 15?

Thanks!!! You just saved me several minutes of internet searching.

 

[JJT-NC]

@millsj I was disconnecting my batteries on my JLUR (with LED tail lights) for years to prevent the DOA battery situation after towing. You can successfully do this by disconnecting both negative cables from the big battery, and keep them isolated from each other and ground. This is, in fact recommended in the owners manual in the 'vehicle storage' section. (I found that the lowes carries a plastic, waterproof cover for connections between outdoor extension cord, and used this to isolate the ends of the negative cables.) I also used wing nuts with lock washers for a quicker connect/disconnect. I lost a lot of wing nuts and lock washers in that engine compartment due to my fumbling fingers.

I recently installed the cool tech LED Light fix, and it works much faster with no fussing - just returned from a 1.500mile 2 day trip and both batteries kept full charge the whole time!

TLDR: You must disconnect both negative cables from the big battery, and keep them isolated from each other and ground, as described in the owners manual for storing the vehicle.

 

[Ronkat]

New to this forum because of this thread all (19 pages)(and others). Thankyou to Cool Tech, mikeq and RubiBlu for all their input and explaining of this Led wake-up problem. Being new to flat towing and Jeep I was getting stressed over stories of dead battery problems now I know how to remedy it. I will be ordering the Cool Tech fix today. Just hope the switch comes with instructions for dummies as I am not electricly inclined. Thanks, Ron.

 

[Oakmanr]

I already have a lot of the components of the CootTech Deluxe kit.

I just found the RVi Towed Battery Charger online for $55. I already have the umbilical they suggest using, so I'm leaning toward that one.

I appreciate your input!

Do you have the factory LED lights? If so you’ll need the cool tech product that addresses this issue.
I have a 2018 jl rubicon with the led package it the above was the only thing that helped with the issue.

 

[mmayer813]

Just to be clear about what causes the Jeep to become awake and consuming power:

Note: This occurs on any Jeep Wrangler or Gladiator that has the REAR OEM LED light option.

The activation of any of the rear lights by a towing harness - regardless of manufacturer/brand will cause the Jeep to come out of sleep mode. This includes the brake lights/turn signals and the running lights.

There are 3 ways to circumvent this problem so that it does not drain your battery;

1. You can install a high-quality battery charger such as the RVi Towed Charger Plus. This will not keep the Jeep from waking up but the charge function should offset the current draw occurring because the Jeep is awake.

2. You can disconnect the fault sense wire from both the left and right rear lights each time you tow. The fault sense wire is what is carrying back a 12v signal to the BCM and causing the Jeep to wake-up. This is an OK solution if you do not tow that often but it is kind of a PITA because you need to re-connect the wire when you are not towing - or you will get a "bulb out" message on your dash display.

3. We have a Battery Drain Fix on our website. Essentially it is just a switch that automates what you can do manually in Step 2, above. This fix is almost trivial to install if you are installing at the same time as our tow harness. Note that the fix WILL work with any tow harness - including MOPAR's own harness solution.... it is just easier to install when installed with our harness because you are in the same area making similar connections.

Question: If I leave the fault sense wires diabled...is there any downside other than a "bulb out" warning?

 

[CoolTech]

Question: If I leave the fault sense wires diabled...is there any downside other than a "bulb out" warning?

Nope... but I suppose that message would get annoying over time? Folk have asked us about forgetting to put the switch (in our solution) in the right position. If you were to jump in the Jeep after disconnecting and forgot to put the switch back to JEEP mode, you'll simply get this bulb-out message. The same thing would happen if someone were to inadvertently flip the switch while you were driving.

 

[mmayer813]

Got it, thank you.

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