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I installed the CoolTech JL Tow Harness Kit in my 2018 JL Wrangler, 2 door. For the first year or so I towed with no problem and then every time I tow the Jeep the Jeep battery is dead at the destination. I've noticed that when just washing the Jeep at a self car wash the Jeep will sometimes "come awake" while washing and I'm thinking that's happening while towing and causing the battery to drain. Anyone have any suggestions on how to stop the Jeep from having it's battery drained while being towed? I've always made sure the ignition if off and have tried leaving the keys in the Jeep and out of the Jeep and still the battery is dead at the destination. I tried contacting CoolTech and they swear it's not their tow harness. They only deal via email and we exchanged a few emails to try and troubleshoot but then they went silent so I'm on my own and very frustrated.
 

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2021 Jeep Wrangler Unlimited Rubicon 3.6L etorque with automatic transmission
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That would be weird if the Tow harness is causing that, but I suppose anything is possible. Speaking of possible are you able to unplug the harness from the fuse box or wherever it is connected just to figure out if that is what is causing the problem?

The other thing you mentioned was when you were at a car wash and washing your Jeep and it would "come alive". The lights come on and doors unlock as a result of the keyless entry from the door handles when water hits them. Mine did that today as I was washing mine as well, and so have a few other vehicles I've owned with keyless entry. In other words it is normal on a keyless entry vehicle for that to happen while washing it, so you can cross that off the check list.

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I installed the CoolTech JL Tow Harness Kit in my 2018 JL Wrangler, 2 door. For the first year or so I towed with no problem and then every time I tow the Jeep the Jeep battery is dead at the destination. I've noticed that when just washing the Jeep at a self car wash the Jeep will sometimes "come awake" while washing and I'm thinking that's happening while towing and causing the battery to drain. Anyone have any suggestions on how to stop the Jeep from having it's battery drained while being towed? I've always made sure the ignition if off and have tried leaving the keys in the Jeep and out of the Jeep and still the battery is dead at the destination. I tried contacting CoolTech and they swear it's not their tow harness. They only deal via email and we exchanged a few emails to try and troubleshoot but then they went silent so I'm on my own and very frustrated.
I read up about this wiring kit. IF, and I mean IF, it was properly installed, then your dead battery shouldn't be caused by towing, however, since you claim it is, then I'd suspect there is an issue with the wiring harness.

As for the jeep "coming alive", it can you reproduce this when you want to, or is it random? What do you mean when you say it's coming alive?
 

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Discussion Starter · #4 ·
That would be weird if the Tow harness is causing that, but I suppose anything is possible. Speaking of possible are you able to unplug the harness from the fuse box or wherever it is connected just to figure out if that is what is causing the problem?

The other thing you mentioned was when you were at a car wash and washing your Jeep and it would "come alive". The lights come on and doors unlock as a result of the keyless entry from the door handles when water hits them. Mine did that today as I was washing mine as well, and so have a few other vehicles I've owned with keyless entry. In other words it is normal on a keyless entry vehicle for that to happen while washing it, so you can cross that off the check list.

Sent from my SM-F916U using Tapatalk
Thanks for the suggestion of disconnecting the harness. It's not possible in the case of the CoolTech harness as it's spiced into the Jeep wiring with a switch to enable towing vs Jeep... flip the switch to Tow when towing and to Jeep when not towing. Also, the water hitting the door handles makes sense ... hadn't thought about that!
 

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Discussion Starter · #5 ·
I read up about this wiring kit. IF, and I mean IF, it was properly installed, then your dead battery shouldn't be caused by towing, however, since you claim it is, then I'd suspect there is an issue with the wiring harness.

As for the jeep "coming alive", it can you reproduce this when you want to, or is it random? What do you mean when you say it's coming alive?
As far as I can tell the wiring harness is installed correctly as it works fine ... with the switch in the "Jeep" position all the lights operate off what is happening in the Jeep such as break lights and turn signal lights and with the switch in the "Tow" position all the lights operate off what the tow vehicle is sending. Or at least it's not obviously installed incorrectly. By "coming alive" I'm referring to the Jeep dash lights up and tail lights and headlights come on.
 

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Thanks for the suggestion of disconnecting the harness. It's not possible in the case of the CoolTech harness as it's spiced into the Jeep wiring with a switch to enable towing vs Jeep...
I built my own version of the CoolTech harness because I couldn't see spending $150 for $20 worth of wiring and a $5 switch. Anyway, the CoolTech harness connects to the Jeep with butt connectors, but I used blade connectors so it's a simple matter of unconnecting it and reconnecting the Jeep's harness - in fact I just did that because we just sold our JKU and I pulled the harness out so I can re-install it in our new JLU when it gets here.
 

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As far as I can tell the wiring harness is installed correctly as it works fine ... with the switch in the "Jeep" position all the lights operate off what is happening in the Jeep such as break lights and turn signal lights and with the switch in the "Tow" position all the lights operate off what the tow vehicle is sending. Or at least it's not obviously installed incorrectly. By "coming alive" I'm referring to the Jeep dash lights up and tail lights and headlights come on.
Sounds more like you hit the key fob. If you didn't, then there is a connection that is not water proof, or water resistant to be proper. It's time for you to have ALL the splices you have installed checked and maybe redone.

Since the harness is connected with an "air gap", a marketing term to mean it uses Optio-Isolation, the lights ARE NOT powered by the tow vehicle, they are powered by the jeeps battery, thus the reason you are seeing the battery die. How long do you tow the jeep for before you turn it one? Do you use daylight running lights on the tow vehicle? Seems to me that the design of the harness is to blame here.
 

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Since the harness is connected with an "air gap", a marketing term to mean it uses Optio-Isolation, the lights ARE NOT powered by the tow vehicle, they are powered by the jeeps battery, thus the reason you are seeing the battery die.
Which harness has this alleged "optio-isolation" and where is it located? Certainly not the CoolTech harness. It is a simple 4PDT switch arrangement - power for the lights comes from either the Jeep itself or the RV, and being a toggle switch it is a "break before make" connection so there is no way for it to get power from both sources simultaneously. The switch is placed in the Jeep's wiring harness where it runs under the front passenger door sill and from there it appears to be a straight shot back to the rear lights.
 

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Which harness has this alleged "optio-isolation" and where is it located? Certainly not the CoolTech harness. It is a simple 4PDT switch arrangement - power for the lights comes from either the Jeep itself or the RV, and being a toggle switch it is a "break before make" connection so there is no way for it to get power from both sources simultaneously. The switch is placed in the Jeep's wiring harness where it runs under the front passenger door sill and from there it appears to be a straight shot back to the rear lights.
Per their website

"Perhaps one of the most frequent question we get from customers is if the Tow Wiring harness is protected using diodes – as no one wants to have back-feeding problems to either the Jeep’s (increasingly complex) wiring or back-feeding to the RV. Our new solution for the JL is one better than that! The analogy that I prefer is in the IT security world (especially with the US military) – and this is the notion of “air gapped”. In the security world, you can talk about all of the precautions, processes, detection and intervention protocols, etc… and the military will just smile at you and insist that the solution is air-gapped. NO physical connections to non-secure environments. We’ve done the same with our new JL-exclusive Tow Wiring solution. It’s air-gapped. There is simply no need to have any conversations about the "amount" or "level" of isolation, if the Jeep electronics are protected sufficiently, or if there can be back-feeding to the RV. It can’t happen."


Being "air gapped" has ZERO to do with a toggle switch, it's a method to isolate electrical signals.


When you Optoisolate a circuit, you are required to provide power from a source that is separate from the line providing the signal; it's ISOLATED. You apply a brake signal, the RV is only telling the Jeep to apply the brake signal, not supplying the Voltage to make the brake lights work, that voltage is supplied by the jeeps battery. Thus probably why the jeeps battery is having issues. How long can your jeep site with the motor off and the lights on?

Diodes only prevent current (voltage) from flowing in a direction you don't want it to - think of them as a one-way gate. As an example, you have a lighted switch that turns on a back up camera, as well as the back up camera is turned on via your back up lights. Unless you use a diode, the power (voltage, Current) that the back up lights use will cause the switch to light up when you are backing up the vehicle. I do this because I want to know there is power in the circuit when I back up, and don't really care if the light in the switch is powered on at that time.
 

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Per their website

"Perhaps one of the most frequent question we get from customers is if the Tow Wiring harness is protected using diodes – as no one wants to have back-feeding problems to either the Jeep’s (increasingly complex) wiring or back-feeding to the RV. Our new solution for the JL is one better than that! The analogy that I prefer is in the IT security world (especially with the US military) – and this is the notion of “air gapped”. In the security world, you can talk about all of the precautions, processes, detection and intervention protocols, etc… and the military will just smile at you and insist that the solution is air-gapped. NO physical connections to non-secure environments. We’ve done the same with our new JL-exclusive Tow Wiring solution. It’s air-gapped. There is simply no need to have any conversations about the "amount" or "level" of isolation, if the Jeep electronics are protected sufficiently, or if there can be back-feeding to the RV. It can’t happen."
But if you continue reading down that statement, it says:

"The best solution are often times the simplest. We’ve achieved an air-gapped solution by using a switch. An easy-to understand concept. EITHER the Jeep is connected to its tail lights OR the MH is connected to the tail lights. Never both. No chance for back-feeds. No chance for one signal to override another. Further, no more complaints about dim taillights due to the inefficiency and inconsistent quality of diodes. We've made it simple. The Jeep is connected to the tail lights OR the Motorhome is."


Being "air gapped" has ZERO to do with a toggle switch, it's a method to isolate electrical signals.
Taking a look at the image of their kit, there in nothing special about it: there's some sheathed wire connected to a 4PDT switch, some metal brackets, tie wraps, butt splices, and a rubber grommet. It's the same as their kit for the JK series, and same as what I built (for about 1/4 the cost) for our JKU, and what will be put into our new JLU when it arrives, and what is currently in our JT. The "air gap" is simply the construction of the 4PDT switch: the center connector on the switch is connected to either the Jeep's wiring or the RV's wiring.

When you Optoisolate a circuit, you are required to provide power from a source that is separate from the line providing the signal; it's ISOLATED. You apply a brake signal, the RV is only telling the Jeep to apply the brake signal, not supplying the Voltage to make the brake lights work, that voltage is supplied by the jeeps battery. Thus probably why the jeeps battery is having issues. How long can your jeep site with the motor off and the lights on?
This is exactly what is happening with the CoolTech harness - it's just a mechanical process instead of an electronic one: the user flips a switch, which triggers a change in the source from the Jeep to the RV, or vice versa.

Diodes only prevent current (voltage) from flowing in a direction you don't want it to - think of them as a one-way gate. As an example, you have a lighted switch that turns on a back up camera, as well as the back up camera is turned on via your back up lights. Unless you use a diode, the power (voltage, Current) that the back up lights use will cause the switch to light up when you are backing up the vehicle. I do this because I want to know there is power in the circuit when I back up, and don't really care if the light in the switch is powered on at that time.
I know how diodes work - I spent about 35 years in the semiconductor industry, involved in the design of both analog and digital integrated circuits. The CoolTech harness is a simple, but efficient, solution to the problem and there is no way for it to draw power from the Jeep's supply if it is installed correctly.
 

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Did you’re Jeep come with LED lights? Here is a known problem with the bulb out circuit (required by the feds) on factory equipped led taillights. Every time the brake light or turn signal comes on, the bulb out circuit is activated which wakes up part of the Jeep’s computer system. That in turn drains the battery. I have the MOPAR tow harness and habe the same problem. I installed a Cooltech harness that gives you the option of disconnecting the bulb out wires thus the Jeep doesn’t wake up. I haven’t had a chance to fully test it yet but will over the next two days.
 

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Which harness has this alleged "optio-isolation" and where is it located? Certainly not the CoolTech harness. It is a simple 4PDT switch arrangement - power for the lights comes from either the Jeep itself or the RV, and being a toggle switch it is a "break before make" connection so there is no way for it to get power from both sources simultaneously. The switch is placed in the Jeep's wiring harness where it runs under the front passenger door sill and from there it appears to be a straight shot back to the rear lights.

2nd Paragraph.

"Our new solution for the JL is one better than that! The analogy that I prefer is in the IT security world (especially with the US military) – and this is the notion of “air gapped”. "
 

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Great pro and con discussion but the op never came back to say what happened.
 

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I can say that after 2 days of towing with the Cooltech switch in tow mode, he Jeep started without a problem. In the past I’d have to jump the Jeep after 2 days. This seems to have solved the problem of the LED light out circuit waking up the computer and this draining the battery.
 
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