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Old 11-18-2017, 09:25 PM   #1
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F-150: 12V on 7 pin connector question

I recently got a new 2017 F-150. I have one of the 7 pin connector testers and when I used it all the pins work except the 12V charging line from the truck. The truck knows a trailer is there because it comes up on the dash. I added a resistor to ground on the 12V pin thinking it may be testing if there is a load, but that did not help. I checked if the LED worked on the tester and it does. The dealer checked it and says it works - it just needs a real trailer and not a tester. Does anyone have experience with this? Do you know what the computer wants to see to turn on the 12V battery charging line on the 7 pin connector?

I could just wait and try it with my trailer (it is put away for the winter) but I would like to understand how it works.

Thoughts welcome.
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Old 11-18-2017, 09:42 PM   #2
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I can tell you that on my 2015, it has what they call a "smart trailer tow connector" if it has the towing package. It won't send power to that pin unless it senses a battery on the other end. A tester won't have that of course, although I suppose with the right resistor it might work. But, not necessary. Once connected to the trailer, that pin should work. You could test with a voltmeter to confirm that once you're hooked up.

On some older model F150s, Ford would provide a plastic bag with a fuse and relay which you would have to install in order to get 12v+ to work.
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Old 11-19-2017, 12:17 AM   #3
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If the truck's electronics are testing for the presence of a trailer battery (not just a trailer), adding a load (such as a resistor to ground) may not do it. Perhaps like most modern battery chargers, the charging circuit doesn't turn on until it sees at least a minimum voltage from the trailer battery.

If you hook up a 12 volt battery to the charging and ground lines, my guess is that the voltage will jump up as the truck turns the charge line on to see the truck's system voltage (which will be more than the battery has by itself).
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Old 11-19-2017, 12:24 AM   #4
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Quote:
Originally Posted by Brian B-P View Post
If you hook up a 12 volt battery to the charging and ground lines, my guess is that the voltage will jump up as the truck turns the charge line on to see the truck's system voltage (which will be more than the battery has by itself).
I'm not really sure how it works, but your guess seems plausible to me. It is checking for a battery on the other end of the charging circuit, not just a trailer connection.
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Old 11-19-2017, 05:22 AM   #5
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Might be like my solar controller where if it sees under a minimum voltage it shuts down, 10v I think.
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Old 11-19-2017, 11:33 AM   #6
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Here is my dealer’s response to this issue on my 2015 F150.

As is suggested, I have found that connecting the trailer with the truck ignition turned off will result in current flowing to the trailer battery once the truck is started. However, as discussed in a previous thread on this issue, the charge current is quite low; certainly not enough to keep the trailer battery charged while running the fridge on 12 volt. My previous tow vehicle, on which the battery charge circuit was wired directly to the truck battery had no problem keeping the trailer battery charged with the fridge on 12 volt. I plan to rewrite this circuit on the F150 before our next camping season.
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Old 11-19-2017, 11:56 AM   #7
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Thanks for the post Eric. Yes, even though the charging circuit "works" when the trailer is connected, that doesn't mean it provides sufficient charging voltage to run 12V systems (like the fridge) when underway.
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Old 11-19-2017, 12:58 PM   #8
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My FX4 Came with a solenoid in the glove box that had to be installed for that to work. You might check in the glove box.


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Old 11-19-2017, 04:35 PM   #9
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My FX4 Came with a solenoid in the glove box that had to be installed for that to work. You might check in the glove box.
Yes, up until the new aluminum body, Ford supplied that and you had to install it to get the charging to work. With the 2015 and newer, and the "smart trailer tow connector" in the towing package, that's no longer the case.
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Old 11-19-2017, 07:33 PM   #10
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I intend to "beef up" the charging circuit also. But I have to figure out how to simulate a trailer (since I don't have a real one convenient to my house) because I want to be able to test it after I modify the truck .

I've tried a load of just a resistor. Next I am going to try giving it a realistic battery voltage at about 10-12V and see if it turns it on. After that I will try a real battery. Other ideas to simulate a trailer?

Thanks for all the thoughts.

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Old 11-19-2017, 11:29 PM   #11
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This topic has been brought up before...I just can’t quickly find it. However I remember someone posted this link which I think is worth a look at...even the comments.
Note that they indicate that the stock power line is used to trigger the relay once the vehicle is put into gear...this may by why when we check for voltage we see nothing...as it is not in gear or it is and we can’t catch the vehicle...
https://youtu.be/kNwC3S3wMi8
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Old 11-20-2017, 05:03 AM   #12
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Originally Posted by Eggscape View Post
This topic has been brought up before...I just can’t quickly find it. However I remember someone posted this link which I think is worth a look at...even the comments.
Note that they indicate that the stock power line is used to trigger the relay once the vehicle is put into gear...this may by why when we check for voltage we see nothing...as it is not in gear or it is and we can’t catch the vehicle...
https://youtu.be/kNwC3S3wMi8
Good memory. I posted the link to that video . That is the modification I (with some "improvements") I hope to do. But first I wanted to see if all the pins worked before I changed anything. Given that the relay is mostly (but not totally) a resistive load, I expected that to turn on the 12V charging line, but it didn't.

But your point is valid. I should add to my list "test it with an actual relay" because evidently it worked for this youtube guy and maybe it will work for me.

Thanks for the ideas. Keep them coming.
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Old 11-20-2017, 11:33 AM   #13
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I am not committed to the idea that it is the load or battery on that pin that triggers the DC to flow. As the truck detects any type of trailer plugged into it...with or without a battery to charge...like a simple utility trailer...I think the truck goes into trailer mode after it senses the trailers lights are plugged in. I think if you plug in a utility trailer that has a 7 pin plug and no battery to charge, you will find the power pin comes alive once the truck is put into gear. Note in one of the comment replies in the article he states the power comes to that pin only after the truck is put into gear and stays on until the truck is then turned off. A lot of testing time could be wasted if the truck was not in gear. Hope this helps.
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Old 11-20-2017, 11:54 AM   #14
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Originally Posted by Eggscape View Post
I am not committed to the idea that it is the load or battery on that pin that triggers the DC to flow. As the truck detects any type of trailer plugged into it...with or without a battery to charge...like a simple utility trailer...I think the truck goes into trailer mode after it senses the trailers lights are plugged in. I think if you plug in a utility trailer that has a 7 pin plug and no battery to charge, you will find the power pin comes alive once the truck is put into gear. Note in one of the comment replies in the article he states the power comes to that pin only after the truck is put into gear and stays on until the truck is then turned off. A lot of testing time could be wasted if the truck was not in gear. Hope this helps.
I agree that is a possibility. In fact, I added a resistor to the brake line to simulate real brakes as well as the resistor on the 12V line. I haven't tried adding loads to all the other pins yet, but I could. Good one to add to the list.

I will note that the truck thinks I have the trailer attached with my tester since the truck says so on the dash. But still no 12V.

I have put it in gear, drove it around.... and still no 12V. I don't have a utility trailer available with a 7pin to try that idea.

Various things I have read have said using brakes is required so I have been doing that as well trying "drive".

I appreciate the ideas. Keep them coming. I am hoping to have time tonight or this weekend to try a couple more things.
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Old 11-20-2017, 01:39 PM   #15
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Turning on the charge line only when trailer brakes are detected makes no sense to me, since a trailer can certainly have a battery which needs charging and not have brakes at all... the majority of 13-foot moulded fiberglass travel trailers would fit in that category (although Escape's 13-foot had brakes, because it is much newer and somewhat heavier than the traditional 13's). Being nonsensical doesn't mean it isn't done, of course, but Ford is usually better than that...

The trailer's lighting load could certainly be used as a presence indication, although the truck would probably only use a short test pulse (as most controllers do to test the brake connection), since always-on trailer lights would not be generally desirable to owners.
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Old 11-20-2017, 02:12 PM   #16
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In an effort to solve a late model Ford owners problem with blowing the fuse that supplies power to the trailer...the answer to our question has been answered in a Ford forum. You need to apply the brakes once the vehicle is running to activate the power wire circuit. It is a good read as it covers topics like missing stuff said to be in the manual. Also the fuse that supply’s the power may not be easy to get while camping out in the sticks. You may want to get one at your leisure.
https://www.ford-trucks.com/forums/1...o-trailer.html
Someone also posted a diagram in that forum.
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Old 12-02-2017, 09:59 PM   #17
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In an effort to solve a late model Ford owners problem with blowing the fuse that supplies power to the trailer...the answer to our question has been answered in a Ford forum. You need to apply the brakes once the vehicle is running to activate the power wire circuit.
I heard about applying the brakes but it didn't work. I finally got it to work by putting a voltage using a resistor divider on the 12V line. I also put a resistor to ground on the trailer brake lines also. Once it saw the voltage it would turn on the power to the 12V line. Interestingly, I tried fairly small value resistors (10's of Ohms) and it worked. I tried fairly high value resistors (1000's of Ohms) and it worked, but an additional message came up on the dash saying that the battery was not charging. So it is fairly intelligent.

I crudely checked the current the original factory setup was capable of by using just a 1 ohm resistor to ground and it was capable of putting out ~10 Amps in that situation. I then hooked up an extra line from the battery with a relay to get more current and it definitely gave more. My test wires and 1ohm resistor are not really capable of giving any accurate measurements. That will have to wait for a real current monitor on a real trailer. I set it up so I can easily switch back and forth between factory and my relay setup.

So the video I shared early is accurate other than for my truck I had to add an additional resistor to get a little voltage on the 12V line so it would turn on.
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Old 12-02-2017, 11:30 PM   #18
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Please keep us informed on your progress as I will be doing something like this next spring.
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