Battery charging while towing

DW and I tow with a 2010 F-150, the day we bought it she noticed a small plastic bag in one of the door pockets. The bag contained an electrical relay and a 30A fuse. We asked the salesman what it was for, he said it was for adding a trailer brake controller, but since our truck came with a factory controller, it was unneeded. Well, if you can't trust a car salesman, who can you trust!

I got the oil in the truck changed a couple of weeks ago, and on a whim I asked the service writer that wrote our ticket up, about the fuse and relay. He said it was something to do with the trailer, but that’s all he knew. At this point I'm thinking that maybe I'm trading at the wrong dealership.

Next I did what I should have done in the first place, and that was to find the answer myself. I signed up on a Ford Truck forum and as soon as I searched for it, I found dozens of people asking the same thing. The answer given 99% of the time was that the fuse and relay were necessary IF you wanted the truck to charge the trailer battery while towing. The explanation that was most given as to why you might not want to do this, was that a tiny handful of trailers used this circuit for something other than battery charging, so to prevent problems, Ford leaves them out. Sounded reasonable to me, but I can't say for sure that's a correct answer.

I looked up the reference in the owner’s manual; it directed me to the fuse panel under the hood. The diagram in the manual listed the missing components clearly as the "Trailer battery charging relay" and the "Trailer battery charging fuse". I easily popped them into the empty sockets that were indicated.

I'm not sure how long Ford has been doing this, I did see one post on the ford truck forum from a guy that said his 2007 was like this, so I assume from that it’s not a new thing that Ford does. I also don't know if any of the other truck manufactures do this as well.

Sometimes I feel like I'm the only one that doesn't know these things, but just in case I decided to share our story with everyone.

Neal

Brake and 12v on Fords

Neal I also drive a Ford F250 diesel and it is factory preped for a towing package. Unless you have a brake controler installed you do not have trailer brakes. Factory package means the wiring is there to install B/C and charge circket. You have to install a brake controler if the factory did not install it and you have to complete the wiring by installing the relays and fuses previded by Ford. This is also true for GM, Dodge, Toyota, and most other mfg. I do not know if they have changed or up dated any of this since I retired in 2005. I sugest you check you owners manual for up to date information on Brakes and Trailer charge circket
Sam Shields

Sam -
That makes total sense, thanks for clearing that up. I bet you had no shortage of loyal customers before you retired, you explain things very well.

Neal

I tow with a 2006 Toyota Tocoma,It came with a factory tow package.The charge led was a 18ga. wire that only put out about 5amps , so towing with the refrigerator on 12v ,I was draining my house batteries. I disconnected that wire, installed a 30amp circuit breaker and a 10ga. wire back to the trailer connector.(The problem I had , the factory 7 pin connector was sealed and I couldn't increase the wire size.) I replaced it with an aftermarket item.I had an aux. terminal & charge terminal that were 12ga. I spliced them together to the 10ga. The trailer pigtail end at the battery box, the aux. wire & charge wire were connected to the battery and I rewired all the ground wires on my 97 towlite with solder on connectors & heat shrink tubing. Les

jimandrobie -

Sorry for the late reply but I was hoping someone that knew the answer would reply. I don't know the answer to the question you asked.. but, I do know how you can find out.

I assume that you have a 7 pin connector. The center pin on a 7 pin connector is called the "Auxillary" connection. This is the connection that charges the trailer battery. With the ignition on, put one end of a tester on the center pin of the trucks connector, and the other end of the tester on the trucks frame, be sure to get a good connection. The result should be that you have battery voltage on your tester. If this test is positve, then the trailer battery is being charged while towing.

Neal

Neal,

You may want to double check that. I believe the #4 terminal is the 12 volt charge line. The center terminal is used for extras like backup lights. I checked that to be sure in the Hi-Lo manual.

Also, when you check for voltage on that terminal you may have to have the ignition turned on and even the engine running on the tow vehicle because that circuit may be going through a relay.

Rich -

Good catch! 6 pin connector uses the center pin, 7 pin connector it is the number 4 pin. Thanks Rich

There are some decent pictures of both of these on the eTrailer site, eTrailer.com

Neal

charging while towing

I used the #4 term. & the #7 term. (since I had no back lights) on my 7 pin connector for delivery of higher charging amps (up to 30 amps) to my trailer house batteries while towing with my refrigerator on 12v.

Tow Vehicle Wiring

Anyone having dealer install there hitch and wiring on there tow vehicle, or doing it yourself, should insist that the negative and positive wires be at least #10 and have a 30 amp fuse, especially if you have a 4 cu ft or larger fridge. Any smaller gauge wire will not supply 12 volts to the fridge while driving. They usually only use heavy enough wire to charge the battery, but it is not up to running the fridge on 12 volts while driving.
I previously had a 95 Tow lite and the wires were # 14 and it was just ok , for the 3cu ft fridge. I now have a 2209 Tow lite with 4cu ft fridge, the # 14 gave less than 12 volts at the fridge, I added a # 10 wire and 30 amp fuse, now have just under 13 volts at the fridge with it running on DC.
In my experience the fridge must have 12+ volts in order to properly run on DC.

When we got my wife an '08 Chevy Tahoe and took it to the RV shop to get a brake controller..they let me know that there were 2 wires under the hood and a fuse missing from the factory installed tow package that were needed to work the brake controller ..the chevy dealer didn't know this and one salesman tried to tell me it was because farmers were using the hitch for power..