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Rivolva's avatar
Rivolva
Explorer
Oct 20, 2020

Ford F150 battery drain when towing Travel Trailer

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!

30 Replies

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  • KD4UPL's avatar
    KD4UPL
    Explorer II
    Oct 21, 2020
    Are you perhaps running your RV's absorption refrigerator on the DC setting?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Oct 21, 2020
    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's avatar
    CA_Traveler
    Explorer III
    Oct 21, 2020
    AC clamp meters are very common as used for AC work, make sure you get one with DC amp capability.
  • Rivolva's avatar
    Rivolva
    Explorer
    Oct 21, 2020
    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's avatar
    CA_Traveler
    Explorer III
    Oct 20, 2020
    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's avatar
    time2roll
    Nomad
    Oct 20, 2020
    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's avatar
    red31
    Explorer
    Oct 20, 2020
    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's avatar
    BFL13
    Explorer II
    Oct 20, 2020
    Brake controller acting funny? Pulling amps but not braking the TT so you'd notice? (WAG)
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Oct 20, 2020
    Rivolva wrote:
    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?

    It could be a dozen different thing. Stop making wild guess and buy a current clamp !

    With no trailer attached, start the engine and place the meter on either the positive or negative battery lead. (It may take 5+ minutes for the reading to stabilize, so be patient !)

    Record the reading. Remove the meter, shut the engine off and connect the trailer. Start the engine and place the meter on the same wire. After waiting for things to stabilize, you should be getting almost the same meter.

    Get out your owners manual and find the page that lists the fuses. Remove any fuse that is associated with the trailer, one at a time, checking the meter each time for a change.

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