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Discussion Starter #1
Can someone tell me if I am correct ? The way I read it , if I install a fuse in spot #27 in the underhood distribution panel I will charge my RV battery when hooked up to my 2018 F350.
 

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You will give power to the battery and it will likely stop or decrease the drain on that battery when trailer is connected to truck while truck is running. The length of wire, truck + trailer, will cause enough voltage drop that a true charging voltage will not get to trailer battery. If battery drops to a lower charge level then the resistance of battery will increase and voltage needs to be over 13.9 to get any real current into battery to reverse sulphation on plates in the cells and restore full charge.
I am not saying that it is bad idea at all, it just will not replace charging the battery on a regular schedule to assure the battery lasts more than 18 months.
 

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Discussion Starter #3
Thanks Jimmy.
I'm mainly interested in maintaining the charge while traveling and using the slide outs on my 5er.
 

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Discussion Starter #5
I did a little more digging and found this info.
2017 trucks equiped with trailer brake control have a trailer tow module.
Once the truck detects a trailer is contected and the brakes have been activated it activates battery charging.
No need for relays and fuses to be installed.
If someone with more knowledge than I have can confirm or debunk this please do so.
Thanks !
 

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I'd like to know that as well. I have always assumed that the battery was always being charged when hooked up. Mine is just the small setup for a breakaway.
 

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On mine I have to hit the brakes (or use the 'brake handles' (paddles) on the brake controller) and then the 'charge' line gets voltage. Don't know why Ford did that but I also don't have the fuse in slot 27 - there is not even the capacity to put anything into that slot.
 

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Is it possibly set up that way so that, even if the trailer batteries are low, there will be enough voltage to actuate the brake-away if the trailer becomes disconnected from the tow vehicle?
 

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Guys the trailer break a way and a trailer battery are 2 different animals.
The break a way it self needs to have the provision to charge the break a way battery, otherwise it will just die eventually, look at your specific break a way battery installation on the trailer.

For the "trailer" battery such as RV or dump trailer the black wire is for charging. But it will only if the trailer provides for charging.
http://www.countrytrailer.com/uploads/7wayplug.pdf
This connection should be hot all the time, you can stick this connection with key off and you should read the same as the battery with a very small voltage drop. If you experiance a 1-2 volt drop that means there is a diode in the circuit to prevent the trailer from discharging the truck batteries, this also will prevent full charge of the trailer battery and hence shorten the life of the trailer battery. But there is a solution.

When the truck is running the voltage rises from the battery 12.8V or so to 13.5 or higher. This is because the alternators put out a float charge above battery voltage. You can buy a switch to replace the diode (or isolator), what this switch does is opens the circuit when voltage drops to battery voltage and only closes when the truck is running, that way the trailer battery can't draw the truck battery down, and the trailer battery gets a full charge when your truck is running.

good luck.
 

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Reconfirmed something interesting about my 2017 F450 two weeks ago. Had to take my coach to the dealer because the batteries were not charging and I couldn't use the level-up system on the trailer - kept getting a low voltage warning on the controller. Long story short - I have been forgetting to use the paddles to test brakes, had gotten into the habit of testing the brakes using the truck's brake pedal. Just hitting the brakes does not activate the charging circuit from the truck to the batteries. I must physically apply the trailer brakes using the built-in brake controller -- what I'll call testing the brakes. Just hitting the brake pedal does apply the brakes just fine but, for whatever reason, does not trip whatever is there to activate the charging line. Dealer mechanic and I tested several things and it was consistent - hit the brakes using the brake pedal -- no power to the batteries in the coach at any time during the run-up; use the brake controller's 'paddles', line becomes charged and remains charged the whole time the truck was running. Shut off the truck, restart it and no power to the batteries again until the paddles were used. Again, mine is a 2017 so maybe the 2018s and 19s are different.
 

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Wow. That is really surprising to me. Why would that be designed that way?

I also never test my trailer brakes with the brake controller. I really only pull one trailer with the same load so once I had the results I wanted, I haven't touched it since. But the only battery on it is the Break-away so perhaps I need to do some testing when it's hooked up again.
 

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Another interesting tid-bit: Neighbor has a 2018 F250 SRW and we tested his a couple of nights ago. As soon as he started his truck, the little test light lit up like a Christmas bulb. Hit the brakes, the other lights lit up, same thing with the signals. So, it appears that on his at least, the power line is on as soon as he starts his engine. The light did remain on for a few minutes after he shut the engine off though. We didn't wait all that long to see if it was the 5 minutes he has his stuff to remain on though. Probably should try to check that some time.
 

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@skypilot. What connector location are you using to test the charging functions?
 

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I have a 2017 F350. I was testing the in bed plug one day to test the trailer battery charge wire's. And it was dead. No Power.
I dug and dug on the internet and found out just what skypilot said. If you don't hit the trailer brake lever to test the brakes it will not start sending power to trailer battery's.
Strange as it is. Now every time I hook up I do a brake test. And alls good.
 

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That is the oddest thing. I just got a 2019. I wonder what that will take to "activate" the trailer battery charging? I guess we'll see once I get everything set up for towing. I'm a little ways from that yet though.
 

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Jesus_Man: Sorry for the delay - been under the weather. The tester was from an RV shop and looked like [ame]https://www.amazon.com/58270-7-Way-Blade-Connector-Tester/dp/B001EOWQY4[/ame] . Bunch of LEDs that lit up when we tested certain things.
 

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