Ford F150 battery drain when towing Travel Trailer

[Rivolva]

Hello,

I recently purchased a 2019 F150 to pull our travel trailer (it has the trailer package). When I pull the trailer long distances (3 hours+ driving) I'm finding that my F150 struggles to start when whenever I shut off the vehicle (such as in gas stations etc).

Recently, I did a 5 hour drive, and 30 mins from home I stopped for gas and the vehicle wouldn't start back up again and had to get AAA to jump me. It seems to me that the battery is getting drained by the trailer.

I've had the battery, starter and alternator on the F150 checked by 2 different people and each time they have passed with no issues.

I do have a rear view camera plugged into the 12v charger within the cab, and sometimes the kids or my wife or I will charge their phone in the cab as well.

If I unplug the trailer and unplug the rear view camera, I have found that the vehicle has a better chance of starting.

I had an older F150 (2004) previously which had no issues like this, we would charge items in the cab and use the rear view camera etc and it would start fine.

I'm trying to figure out where the source of the problem may lie, any ideas? Could the battery on the trailer be an issue? Could the wiring harness on the F150 be at fault? Is there an issue with newer F150s being able to handle charging devices as well as the trailer?

Any thoughts would be greatly appreciated!

Cheers!

[red31]

Pulling the 3 wire pin on the alternator and it goes into 13.8v default mode, smart charging disabled.

[time2roll]

Rivolva wrote:
I've had the battery, starter and alternator on the F150 checked by 2 different people and each time they have passed with no issues.

The trick is to test it when the fault actually is occurring.

Did AAA check the voltage etc or just jump and go?

[mr_andyj]

Agree. The trailer simply cannot draw enough amps through that long run of small wire to drain a vehicle battery that is inches from a 140 amp alternator.

A camera or some phones will not draw down a running vehicle battery either.

In the meantime, you might can just disconnect the charging wire that feeds the trailer battery, or pull the fuse if the trailer has one between the battery and the 7-pin plug.
My trailer has solar, so I rarely ever have the vehicle charge the trailer.

Whatever the guy in the above post was talking about with the alternator and the C pin might be the best place to start.

To run a battery down takes some serious work, so the alternator must be at fault (not charging). When alternators die the ECU (trucks computer) and the blower vent fan will run the battery down in 30-45 mins, so your alternator must be putting out some charge that you can go 3-5 hours without the battery being dead.
The camper's battery could possibly contribute voltage back to a dying vehicle battery, but not significant through that long run of small gauge wire.

None of this helps any except to help you eliminate some possibilities and push you towards looking at the alternator first.

[Mike134]

I also have a '19 F150. Has the dealer found any trouble codes? I'd suggest using the Ford roadside service that comes with the truck next time so you can better document your troubles.
I'm guessing your still under your 36/36,000 bumper to bumper warranty?
Doesn't matter if you bought it used coverage still applies.

[prichardson]

What is the condition of the battery on the TT. If it is deeply discharged or shorted it will draw down any other battery (ie the truck battery) connected to it.

[dougrainer]

KD4UPL wrote:
Are you perhaps running your RV's absorption refrigerator on the DC setting?

If he had a 12 volt 3 way, it would NOT drain the Ford Battery. The plain fact is, the FORD Charge system should keep the FORD battery charged while in transit. It is NOT, The trailer will not drain a GOOD battery in 3 to 5 hours. Remember, he also has a COACH battery that is hopefully fully charged when he starts out. He has a FORD charge system problem. Doug

[midnightsadie]

x2

[KD4UPL]

Are you perhaps running your RV's absorption refrigerator on the DC setting?

[MEXICOWANDERER]

That truck is incapable of having an alternator smaller than 95 amps and most likely it is a 140-amp large frame model.

I see posts above that suggest checking amperage between truck and towed vehicle.

140 amps?

Connect trailer to truck. Then measure truck battery voltage. Low? You bet. Check trailer battery. It's either static or losing voltage very slowly.

The alternator isn't charging when the towed vehicle is plugged in. It isn't a drain; it is an intermittant fault. It's time to take it to a *specialist* or to the Ford dealership. The harness under the hood is miswired. The voltage regulator should be in the computer.

Say these words to the service writer "Alternator stops charging when trailer is connected" Simulating the problem can itself be difficult. It may be that an appreance of voltage at a misconnected wire up front shuts down the "C" wire function that runs between the alternator and vehicle ECM. That among a hundred other things will shut down alternator charging. The tech needs to do a point-by-point process of elimination. If the charging connections were done by the previous owner. A good tech can spot it in ten seconds. If the mistake was done by Ford, smile, it'll be their nickle, start to finish.

Use the volts selection on your new clamp-meter.

[CA_Traveler]

AC clamp meters are very common as used for AC work, make sure you get one with DC amp capability.

[Rivolva]

Sounds like I need to buy a DC Clamp meter.

The truck has no issues with the trailer disconnected, no matter how far I drive it.

The two people that tested the battery/alternator/starter did not put any kind of load on it as far as I know, one test was at Autozone and the other at a local Service station, they just used their testing device on the truck battery to confirm that it "passed" their test.

Thanks for the responses

[CA_Traveler]

X2 for a DC clamp on ammeter and voltmeter. Check the battery voltage at high idle with the trailer attached. Check the amp draw on the trailer wire. Load test the truck and trailer batteries.

Maintaining the truck battery should be a non issue for the alternator. If the trailer draws to many amps the truck fuse to the trailer should blow, check to see what size is currently installed.

Did your "people testers" apply a significant load to the truck battery to confirm that it's being charged at the maximum? Unless you know for absolute certain that the truck battery and alternator are good...

[time2roll]

So have you been on a three hour drive without the trailer and no issues?

I would be leaving the truck running and check the truck battery voltage. Check direct on the battery terminals and check on the connectors. s/b the same and more than 13.2 volts. Post the results.

Then shut down the truck and check again. When it fails again check voltage while cranking. Post all results.

I recommend to carry a jump box while this issue persists.

I really doubt it is the trailer.

[red31]

I've used a cig lighter volt meter to monitor the regulated voltage control's wild swings (modes) in voltage of a GM S-10.

[BFL13]

Brake controller acting funny? Pulling amps but not braking the TT so you'd notice? (WAG)