Tow Vehicle has a Weak Starting Crank

[Gliddenwoods]

I tow with a 2019 Ford F-150 and have the 640 AH lithium batteries. Sometimes (not always) when I start my F-150 when towing the truck has a weak crank/battery but (so far) always starts. Since I have 640 AH lithium batteries the truck alternator is not used to charge the batteries. The running lights of the Oliver do draw the charge from the truck, but seems unlikely being enough of a draw to weaken the truck battery. The truck battery is less than two years old and tests Ok.

So, what are the potential causes of the towing truck weak battery{?} and weak start cranking? Need larger battery? Need new or alternator or high capacity alternator?  What is your guess? Has anyone else experience weaking starting crank when towing an Oliver Travel Trailer?

[jd1923]

1 hour ago, Gliddenwoods said:

The running lights of the Oliver do draw the charge from the truck, but seems unlikely being enough of a draw to weaken the truck battery.

This only occurs when you're connected/towing and should not be an issue, given engine runing, alternator charging.

Ever test voltage after your truck has been sitting for 24-28 hours? This would be a first step. You need to get your truck diagnosed independent of the Oliver. Your truck being weak starting could be battery, starter motor, ground or an assortment of issues (again nothing to do with the Oliver).

Best wishes, JD 

[Steph and Dud B]

Does the truck start fine when not towing? 

[Gliddenwoods]

21 minutes ago, Steph and Dud B said:

Does the truck start fine when not towing? 

Yes

[CRM]

2 hours ago, Gliddenwoods said:

I tow with a 2019 Ford F-150 and have the 640 AH lithium batteries. Sometimes (not always) when I start my F-150 when towing the truck has a weak crank/battery but (so far) always starts. Since I have 640 AH lithium batteries the truck alternator is not used to charge the batteries. The running lights of the Oliver do draw the charge from the truck, but seems unlikely being enough of a draw to weaken the truck battery. The truck battery is less than two years old and tests Ok.

So, what are the potential causes of the towing truck weak battery{?} and weak start cranking? Need larger battery? Need new or alternator or high capacity alternator?  What is your guess? Has anyone else experience weaking starting crank when towing an Oliver Travel Trailer?

Since it only happens while towing, the first thing I would check is to make sure that the charge/aux wire isn't connected to the trailer batteries. I see you have the lithium platinum package so it shouldn't be, but I would check that first anyway to confirm. 

[Steph and Dud B]

7 minutes ago, Gliddenwoods said:

29 minutes ago, Steph and Dud B said:

Does the truck start fine when not towing? 

Yes

Weird. So we're looking for a large parasitic draw only when the trailer is plugged into the truck? Things that come to mind: a short in the trailer somewhere, a problem with the trailer brake system, and a long shot. You have the lithium system and lithiums are very good at taking a charge. If your lithium batteries are at a lower voltage than your vehicle battery and IF, somehow, the two systems were connected, your truck battery could be trying to charge your lithiums. But, that's a real long shot, especially if this is a new problem you haven't seen before and you haven't made any changes to the electrical system. One way to find out. With the trailer disconnected, check for 12V on the trailer's Aux 12v Power pin. It shouldn't be there with the lithium package. 

[bugeyedriver]

My TV is a 2018 F150 5.0L V8 with 76,000 miles. (32,000 miles towing)  Over the years, I have also experienced rare slow crank during startups.  One time, I even replaced my battery even though the mechanic said it appeared to be OK.  (Dang!).  I'm up in Canada now and recently went through some slow and painful rush hour traffic in Vancouver for over 45 minutes. after exiting the traffic jam, I pulled over at a rest stop and shut off the engine for about 5 minutes.  during the restart, all I heard was one - single - crank - of the engine and nothing else, over and over again. Crap!  Engine temp gauge appeared normal. Eventually, I called roadside assistance and the helpful responder arrived 45 minutes later, and with his electronic wizardry, he checked out my battery and alternator, both checked out great.  Battery had 12.4 volts and alternator was charging normally.

Before having him attach his jumper cables, I attempted a start on my own, and whattaya know, she cranked up instantly.  Go figure. I thanked the mechanic and gave him rave reviews online.  Now I'm wondering if time passed allowed the starter to cool down enough for a normal start.

After a dive into the F150 chat rooms / forums, I've learned there may be a weakness in these starters when they have been overheated, such as might occur through towing in warm stop and go traffic for a long time.  Hmmmmmmmmmm, 

After returning home in about 2 months, I will take a much deeper dive into this situation and consider another starter, of a different type, that will work for this application.  I also intend to disable the auto-stop feature when not towing (it is already disabled during towing) to limit the cycles on the starter.

Edited August 17 by bugeyedriver

[Gliddenwoods]

7 hours ago, CRM said:

Since it only happens while towing, the first thing I would check is to make sure that the charge/aux wire isn't connected to the trailer batteries. I see you have the lithium platinum package so it shouldn't be, but I would check that first anyway to confirm. 

How does one do your recommendation?

[CRM]

1 hour ago, Gliddenwoods said:

How does one do your recommendation?

Put a test light between the ground and Aux on the trailer connector.

You should get no light, and if you do, the Aux wire is incorrectly connected to the battery

[mossemi]

Have you tried disconnecting the Ollie from the TV when this condition occurs?

Mossey

[Gliddenwoods]

22 minutes ago, mossemi said:

Have you tried disconnecting the Ollie from the TV when this condition occurs?

Mossey

No

[Gliddenwoods]

Just now, Gliddenwoods said:

No

No....but after camp setup and driving around the next day all appears OK

[jd1923]

4 hours ago, Gliddenwoods said:

No....but after camp setup and driving around the next day all appears OK

This means your truck alternator and starter batteries are fine.

What is the SOC% of your LiFePO$ House Batteries when starting attached is an issue?

5 hours ago, CRM said:

Put a test light between the ground and Aux on the trailer connector.

You really need to test. It reads like this wire is hot, connected to your house batteries (shown RED in the picture, but it's the BLACK wire in the Oliver trailer harness).

If it is, and until you can correct this, you need to disconnect the trailer harness whenever your truck engine is off for more than a short break.

Anybody that does not have a multimeter and knows how to use it, should get a test light and learn to use it. This is all you need for this test (plus maybe a nail to use as a second pointer to touch inside the harness coupler):
https://www.amazon.com/WINAMOO-Premium-Automotive-Extended-Circuits/dp/B08D9RY532/?th=1

[mossemi]

18 hours ago, jd1923 said:

You really need to test. It reads like this wire is hot, connected to your house batteries (shown RED in the picture, but it's the BLACK wire in the Oliver trailer harness).

The picture below is from the 2017 OTT LE2 manual.

Mossey

[ScubaRx]

On 8/17/2025 at 5:58 AM, Gliddenwoods said:

How does one do your recommendation?

General Motors trucks actually have a fuse under the hood to disconnect charging power to the trailer batteries. Perhaps Ford’s do also. Otherwise, you’ll have to disconnect it on the trailer side. 

[Gliddenwoods]

Appt at the Ford garage tomorrow.

Thanks for all the input.

[Steph and Dud B]

17 minutes ago, ScubaRx said:

General Motors trucks actually have a fuse under the hood to disconnect charging power to the trailer batteries.

Some vehicles have a fuse, others a relay tied to the ignition circuit. I always unplug the trailer connector from the truck if we spend the night hitched. Just in case.

[ScubaRx]

20 hours ago, Steph and Dud B said:

Some vehicles have a fuse, others a relay tied to the ignition circuit. I always unplug the trailer connector from the truck if we spend the night hitched. Just in case.

What I was referring to was for those that want to easily disable the charging wire from the tow to the trailer without having to cut any wires. 

[Steph and Dud B]

1 hour ago, ScubaRx said:

What I was referring to was for those that want to easily disable the charging wire from the tow to the trailer without having to cut any wires. 

That would work with a relay, too. They're usually plug-in relays under the hood.

[Gliddenwoods]

New Starter.

Diagnostic port code P06E9.

Real hot weather (SW USA camping trips) reported as additional P06E9 performance impact in powertrain control module.

[CRM]

On 8/23/2025 at 6:33 PM, Gliddenwoods said:

New Starter.

Diagnostic port code P06E9.

Real hot weather (SW USA camping trips) reported as additional P06E9 performance impact in powertrain control module.

Strange that it only happened while connected to the trailer... 

[jd1923]

1 hour ago, CRM said:

Strange that it only happened while connected to the trailer... 

Likely not, when first hitched. However after towing, the engine, trans, everything connected and under the hood gets very hot! The hot starter armature and battery cables will create resistance requiring more current to turn and start than when cold. Also as the starter armature gets fried, carbon buildup will also create mechanical resistance requiring more current to turn.

Given the new starter resolves this issue, it shows the starter was on its way out and soon or later would not start the engine even when cold.

[CRM]

5 hours ago, jd1923 said:

Likely not, when first hitched. However after towing, the engine, trans, everything connected and under the hood gets very hot! The hot starter armature and battery cables will create resistance requiring more current to turn and start than when cold. Also as the starter armature gets fried, carbon buildup will also create mechanical resistance requiring more current to turn.

Given the new starter resolves this issue, it shows the starter was on its way out and soon or later would not start the engine even when cold.

Yeah, makes total sense if it happens right after stopping while towing. I was under the impression that the starting issue was when it sat while connected