JLUR battery flatlining when flat towing

[Eder]

OK,,,I have 12v charge link powered by my motor home running to the Wangler Rubicon battery and tested with meter...its getting 12v.

Battery still getting discharged. Today I disconnected the negative terminal to Jeep before hooking up. Once I start the motor home I checked the 12v charge link , it was on. Amazingly my unlock and lock for the Jeep doors worked. If I unplugged the Jeep from the motor home the key fob would not work.

Towed the Jeep a few hours,,,,tire pressure monitoring fault came up when I started the Jeep...Jeep was still discharging during the tow period...whats going on?

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[ekim]

That seems strange. If the negative was disconnected then the battery seems to have discharged on its own. Try disconnecting the negative cable overnight and see if the battery voltage drops in the morning.

 

[dapipp]

While I am not an expert by any stretch there are two batteries. I would think you would need to pull the negative terminal on both to get an accurate test.

 

[Gaffer]

OK,,,I have 12v charge link powered by my motor home running to the Wangler Rubicon battery and tested with meter...its getting 12v.

Battery still getting discharged. Today I disconnected the negative terminal to Jeep before hooking up. Once I start the motor home I checked the 12v charge link , it was on. Amazingly my unlock and lock for the Jeep doors worked. If I unplugged the Jeep from the motor home the key fob would not work.

Towed the Jeep a few hours,,,,tire pressure monitoring fault came up when I started the Jeep...Jeep was still discharging during the tow period...whats going on?

Do you have LED tail lights?

 

[Eder]

I do have LED lights...I did disconnect the grey wires from the tail lights...ended up not working.
I'll try disconnecting the battery post overnight... I never have a discharge trouble except when towing...thought the trickle charge would take care of it but nope!

 

[Down South]

I do have LED lights...I did disconnect the grey wires from the tail lights...ended up not working.
I'll try disconnecting the battery post overnight... I never have a discharge trouble except when towing...thought the trickle charge would take care of it but nope!

Something is not right. I tow my JL with LED tail lights often. I don't disconnect anything. I use a charge wire from the motorhome to maintain the Jeep batteries. I have a Demco Stay-In-Play Duo towed vehicle brake system that is powered by the jeep battery. Other than that, the computer wakes up if I brake or use turn signals.

What is your JL battery powering when towing?
Have you checked, with the Jeep shut off and hooked to the motorhome and motorhome shut down, hook your meter up to the Jeep battery. Your meter should read about 12.6V-12.7V if the Jeep battery is fully charged.
Crank the motorhome and see if the Jeep battery voltage rises above what the voltage was before you cranked the motorhome.

I don't know what you are using for a charge line to the JL. Is it one of the trickle chargers? My setup is a #10 wire from the motorhome to a diode mounted near the Jeep battery and a fuse right at where the charge wire is hooked to the positive terminal on the Jeep battery.

Even without a charge wire, your Jeep battery shouldn't be drained enough to matter after just a few hours of towing.

 

[JeffSFL]

Confirmed. It's the communication back to the BCM through the fault-sense wire.

I removed both taillights and applied brakes on the RV. Jeep did not wake up.

Removed the fault-sense pin from the harness, reattached the lights and applied the brakes. Jeep did not wake up. Taillights and turn signals worked when actuated.

Re-installed the fault-sense pin, put the brakes on the in the RV, Jeep woke up.

Interestingly enough, when the brake pedal is pushed through the window with a broom handle, the pedal doesn't trigger the brake lights. It seems like the Jeep is smart enough to ignore the pedal press when it's asleep but not smart enough to ignore the fault.

I'm assuming this is because the circuit board in the LED taillight is alive from the 12v supplied by the RV and it initiates the signal.


I don't know what the legality or other impacts might be for doing this. This was just for diagnostic purposes.

On the LED taillight assembly:

remove the white cover
push the pin show forward out of the connector for the gray wire
rotate the pin 180 degrees
pull it back down into the connector to where it sits far below the other pins.

@mikeq i registered for this forum just to thank you for this. I just completed a 4,000 road trip flat towing the Jeep behind the motorhome. On the way out by the time I got to Denver the Jeep was dead on arrival. I started searching for answers, certainly, I was not alone in my experience. I found you, and your solution. I also found @CoolTech' switch solution, but I was on the road and had no way to order and have it delivered. So I deployed your fix and it worked masterfully. It was easy to do.

From Denver to Tuscon and back to Wisconsin the Jeep performed as expected but only because of your fix. Started up every time. Now that I"m back I'm considering the CoolTech switch solution simply because it would be easier than pulling the tail lights for every trip. I do get the taillight out warning on the message center when I'm driving the Jeep.

So thank you for your solution! You saved me a ton of frustration

 

[CoolTech]

Jeff, thanks for taking the time to register and make this post. We DO have many, many customers who have had the batter drain and then installed our kit to correct the problem. You are just doing the manual version!! Travel safe!

 

[Rhinebeck01]

@mikeq i registered for this forum just to thank you for this. I just completed a 4,000 road trip flat towing the Jeep behind the motorhome. On the way out by the time I got to Denver the Jeep was dead on arrival. I started searching for answers, certainly, I was not alone in my experience. I found you, and your solution. I also found @CoolTech' switch solution, but I was on the road and had no way to order and have it delivered. So I deployed your fix and it worked masterfully. It was easy to do.

From Denver to Tuscon and back to Wisconsin the Jeep performed as expected but only because of your fix. Started up every time. Now that I"m back I'm considering the CoolTech switch solution simply because it would be easier than pulling the tail lights for every trip. I do get the taillight out warning on the message center when I'm driving the Jeep.

So thank you for your solution! You saved me a ton of frustration

in April of 2007 ... Yup, 2007, Clayton's assistance saved me "a ton of frustration" just like he did for you....

He assisted/advised me ...and then I went with one of his terrific product offerings in 2007.

I have also purchased some of his offerings since then. Top notch are his offerings / they work as advertised..

Anyway, you picked the right guy to get advice from. Clayton knows his stuff..

@JeffSFL ....Real nice you went to the trouble to register with this forum, just. so you could Thank, Kendall @CoolTech..

.

 

[JeffSFL]

Jeff, thanks for taking the time to register and make this post. We DO have many, many customers who have had the batter drain and then installed our kit to correct the problem. You are just doing the manual version!! Travel safe!

Thanks, Kendall. I'll be ordering your more "elegant" and simple fix than the manual version soon. If my memory is correct it was only about $40. A small price to pay for the convenience. Thanks for creating such a simple solution. Surprised that Jeep isn't aware of, or worse, maybe doesn't care about this, since their products are the top-recommended flat tow option...

Thanks again for all the help, love this forum.

 

[mikeq]

@mikeq i registered for this forum just to thank you for this. I just completed a 4,000 road trip flat towing the Jeep behind the motorhome. On the way out by the time I got to Denver the Jeep was dead on arrival. I started searching for answers, certainly, I was not alone in my experience. I found you, and your solution. I also found @CoolTech' switch solution, but I was on the road and had no way to order and have it delivered. So I deployed your fix and it worked masterfully. It was easy to do.

From Denver to Tuscon and back to Wisconsin the Jeep performed as expected but only because of your fix. Started up every time. Now that I"m back I'm considering the CoolTech switch solution simply because it would be easier than pulling the tail lights for every trip. I do get the taillight out warning on the message center when I'm driving the Jeep.

So thank you for your solution! You saved me a ton of frustration

Glad to help. It drove me nuts the first trip. Had to disconnect the battery every leg of our 2.5 month trip. Started diagnosing the issue when we got back. I'm happy that people are helped by this and this is the true beauty of forums and communities like this.

I've been helped on numerous forums for various issues and it's an honor to be able to pay back in some small way.

 

[Gaffer]

I found this link very good to explain the cooltech install and thus eliminate the diodes.

So in this video there is a red wire that was unused. What is the red wire for? Anyone have the harness instructions that they could post or send via message?

 

[CoolTech]

The red wire was originally included in approximately the first dozen harnesses that we sold. The last several hundred were sold WITHOUT the red wire.

We had the best of intentions with the red wire. Some aux brake controllers want to see a (+) 12v signal when the brake pedal is pressed. In order to help owners installing our harness (and to provide further differentiation) we had this "pigtail" red wire that could be used. The problem is that the Jeep we used for development and pre-production programming. In production Jeep JL's, the Jeep goes to sleep-mode a couple of minutes after the last door is closed.... and there is no 12v brake signal to pass-thru. As such, the wire was useless and eliminated from the kit.

 

[Gaffer]

Thanks. I thought maybe it was 12 v supply for the RVI battery tender

 

[garykk]

Just thought I would add something to this discussion. I have towed several different vehicles behind my RV, GMC, JEEPS, and FORD. I have found that the 12 volt charge line from the RV just does not provide enough for these newer vehicles with their power draw. I found and use a Toad Charge. It will supply up to 10 amps of 12 volts to your towed vehicle. It’s protected with circuit breakers and will not allow feed back when your Rv is parked.
Works for me.
http://www.lslproducts.net/ToadChargePage.html

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