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Dingy towing a 2019 Lincoln MKZ Hybrid

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Hi All,
Hope everyone is staying well out there.
This question has to do with dingy towing a 2019 Lincoln MKZ Hybrid behind my 2002 Tradewinds LTC.
This car supports a "stay in neutral" mode for all 4 down towing.
Does anyone have a suggestion as to avoid the problem I'm having?
Here comes the nitty gritty details.  Thanks in advance for any tips you may have!
1) The car runs and starts just fine when not towing.
2) I have the +12v charge line from the motorhome starter batteries connected to the starter battery of the car via a 30 amp auto-reset circuit breaker.
After towing for a about 4 hours, we found that the car had gone into the "deep sleep state" that naturally occurs when the battery voltage drops too far.
While the car was still in "stay in neutral" mode, the doors were locked.  I had to use the valet key to get in.
The battery was so discharged that I couldn't start the car.  Had to jump it.
I contacted Lincoln, and had them escalate the issue to engineering, but didn't get any useful information.
I have heard that some hybrids can be problematic when being towed like this.
I have now installed a voltage monitor with Bluetooth radio that allows me to easily monitor the car battery voltage in real time.
Here's a datalog from that system of the battery voltage during a startup and shutdown event (normal driving not towing).
This is the expected voltage variance when operating the car by itself.
Inline image

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Welcome to the FMCA Forum.

What gauge wire are you running from coach chassis battery to toad battery?  Both positive and ground?

Have you measured voltage at the toad battery with the coach engine running?

I am asking, because a 30 amp breaker (and of course wire sized to convey it) should well more than keep up with your toad's energy requirements.

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Do you have a Toad charge in the system. Mine regulates the charging and never had an issue with our MKX. Maybe that auto-resettable breaker is constantly tripping and not charging like you think it is.

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Thanks guys for your kind replies!  Since I posted, I discovered something very interesting.

Stumbled upon a youtube video done by Lincoln on Towing the 2017 MKZ.

It showed that when you put the car into stay in neutral mode, you then then turn it off.  Well, it's not totally off, but shuts down non-essential power.

I then researched the owner's manuals for the 2018-2020 MKZ Hybrids.  The '18 and the '20 match my '19 manual, which does NOT mention turning off the car after putting it into stay-in-neutral.

OK, so I ran an experiment.  Put the car in stay-in-neutral mode, but didn't hook it to my motorhome at all.  Turned it off, and left it for 8.5 hours.  I watched the battery voltage over that time, and it only dropped 22mV.  The car fired right up like nobody's business.

I'll contact Lincoln again and ask them whether the 2018-2020 manuals are in error.

If so, there is really no need to even have the car battery on a float charge from the motorhome, as long as you fire it up after each day's towing (which you should do anyway to stir the tranny fluid etc).

I'm a retired electrical engineer (Silicon Valley chip designer), so I also checked the impedance between the car starter battery ground post and the chassis of the car.  Guess what, they aren't exactly the same thing!  I'm guessing that has to do with the low-voltage and high-voltage battery management in the car.


Here's the youtube link of the video -


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Oh, to answer your questions, I have 12 ga wire all the way from the coach to the car battery + post.

And I was not using any smart controller in the system.

The charging current was between 4A and 11A depending upon the state of the car.  I also had replaced the 30A breaker with a new one.

However, based upon what I describe in my 2nd post, I don't think it will matter now.  As long as Lincoln approves the 2017 tow mode method for the 2019 model, I'll just disconnect the TOAD charge line. 

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Off topic, but I discovered that the User Manual for a 2002 National Tradewinds LTC is incorrect in terms of the exhaust brake switch location.

Mine has no labels on the switches, just the graphics.  The exhaust brake is an "M" with a circle around it.

My manual shows it as the 3rd toggle switch from the left, but it turns out that it's the 1st switch location. This, in addition to a missing fuse, caused my grief with the jake brake.

Thanks to excellent troubleshooting by my local truck repair facility, it's all good now!

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