Dennism1

I bought a new f150 with full tow package to pull my trailer. I tested the 7 way plug with a tester and all lights worked except the 12V slot which leads me to believe there is no power going back to charge the trailer battery

Bruceman53

You should have a relay and small wiring harness for your brake controller in the glove box.


The relay plugs into the fuse panel and prevents the trailer from drawing from the truck when its not running. (isolator)

Irish Kid

Depends on how your trailer is wired but no matter even if it is charging it will not be much just a trickle. Your truck alternator doesn't know that is supposed to charge TT battery so all its efforts go to the TV battery.

larry2c

I don't know what all model years this applies to but it seems Ford made a decision to NOT install the relay and fuse that sends power to the 7 way connector. There are a lot of threads on this that will tell you which relay and fuse is not there or you can look in your owners manual to see which ones are used for this and then look in your fuse panel to verify if they are there or not. Mine were not there and I had to purchase and install them. Not a big deal but it seems pretty cheesy to me to not install $5 worth of parts on a $40K vehicle...

PerryB

The reason the trailer only gets a few amps is because the current has to travel down a relatively long path and it's usually only a 14 ga. conductor. An alternator doesn't "know" anything and has no control over where the current flows. It puts out a constant voltage and current flow is a result of where any relative potential lies.

Mulestang

Check the owner's manual. In the passenger side kick panel fuse box, there will be a "trailer tow battery charge relay" slot. Either your relay is bad, or most likely, not there. Most auto parts stores will carry the relay, but I sucked it up and paid extra for the OEM.

smokeywren

If your F-150 is new and not just new to you, then your Ford dealers service department didn't do a good job of the pre-delivery inspection (PDI). Your new truck came with a plastic bag in the glove box containing fuse(s) and relay(s) that the PDI tech was supposed to install to make the trailer battery power wire "hot".


If that bag containing at least one fuse and relay is still in the glovebox, then it's easy for you to DIY. Your F-150 has two "fuse panels", one in the passenger's footwell and the other under the hood near the radiator tank. The one under the hood is called a power distribution box. Look in your Owner's Guide for the fuse/relay diagram to see where in the power distribution box to install the fuse and relay for "TT battery charge relay" . Mine is in the "Roadside emergencies" area of my 2012 Owner's Guide.

Buzam

Can anyone confirm if this is still the case with the 2015+ trucks. My 2011 came with the fuse and relay in the glove box, but my 2016 did not, I have been going on the assumption the were already installed on the new trucks.

Ricktwuhk

2016 and newer have no relay. Posted many times. It is intelligent and has to see a load. Hook it to the trailer, start truck, and you should see a message about the trailer being connected.

It will top off the trailer battery. It will NOT charge a very low battery.

techrep

iTrader: (1)

Their are fuses involved also..