Electrical question....

[9thousandfeet]

Seems like "towing and hauling" might be the right forum for this question, but I'm not sure....

OK, so if I connect a camper trailer (or a slide-in camper for that matter) to the truck ( 2018 3500 Tradesman 6.4) via the 7-pin plug in the truck's trailer wiring harness - then I'll get the camper running lights and all the rest, along with a hot and neutral through which the truck alternator can provide charging to the camper battery bank while driving down the road.

So far so good.

Now, I was told by a guy at an RV place that some of the new trucks have a built-in provision which will prevent the truck battery from being drained by demand from the camper/trailer when the rig is parked (for the night, say) —without the need to physically disconnect anything and without having to install any automatic disconnect - like an ignition-actuated solenoid or something.

Anyone know if the 2018 3500's are set up this way through in the trailer wiring harness?

Or will I have to either install something to automatically protect the truck battery from discharge, or manually unplug the camper from the truck to prevent the camper from pulling current from the truck starting battery?

I just spent more than an hour on the phone trying to track down solid information on this, first with an RV place, then the camper manufacturer, and then with the Ram dealership.
At this point all I know for sure is that the camper system doesn't provide automatic protection for the truck battery, so either the new truck already will, or I'll have to set it up somehow to make it so it does.

 

[Ratket]

Personally I would just set it up your self so you never have to question it or worry about it.

 

[9thousandfeet]

Personally I would just set it up your self so you never have to question it or worry about it.

I'll be happy to do that if necessary, but that brings up the question of the best way, and the safest way, to do it.
On our 2000 Tundra which we used to use for a small camper, I put an ignition actuated solenoid which physically disconnected the camper electrics from the vehicle electrics, and I'll be OK with doing that in this case too, just so long as installing a device like that doesn't cause any problems with the truck electrical system, which is way the heck more complex that an almost 20 year-old Tundra.

What I don't want to do is take a guess at how to resolve this problem and end up with something that creates conflict with the truck factory electrics.

 

[Cardhu]

check and see if it works as predicted.

Put a Volt meter on your truck battery and have somebody turn on some DC appliances in your camper, like the water pump. Check it again in 20 min, 30 min, hour, etc for isolation. I assume if it exists it would be like when your interior dome light turns off when you leave the doors open for 15 min.

Your looking for voltage drop on your trucks battery when the water pump kicks in. Right after you shut down it should show a drop when you turn on the water pump if its hot to the trailer 12V system. confirm.

If it disconnects, when you do it again at different times, it should be isolated and no voltage drop at truck and running off the house battery.

Otherwise, disconnect and plug it back in when you do your walk around before departure. Put equipment status tag on your steering wheel if you feel you will forget.

 

[9thousandfeet]

I assume if it exists it would be like when your interior dome light turns off when you leave the doors open for 15 min.

Now that's a good thought.
It would make good design sense for the truck to turn off all non-essential battery loading automatically after a set time, be it lights left on or a drain via the trailer harness or anything else.

And your plan to establish if that's happening or not using battery voltage fluctuation in real time while toggling camper appliances on and off is good too, so thanks for that.

The truck is still on a train somewhere between Saltillo and Denver, last I checked, so I'll have to wait. But it's good to have a plan of attack.

Many thanks.

 

[csuder99]

Unless something changed in the last year or two pin 4 is always 'hot' on RAM trucks. It is true that some manufacturers turn off that pin when the engine isn't running.
The easiest way to check is to turn off the truck, let it sit for a few minutes and check if pin 4 has 12V. Most likely it will.

 

[9thousandfeet]

Unless something changed in the last year or two pin 4 is always 'hot' on RAM trucks. It is true that some manufacturers turn off that pin when the engine isn't running.
The easiest way to check is to turn off the truck, let it sit for a few minutes and check if pin 4 has 12V. Most likely it will.

Yeah.
I've been overthinking this.
It really is that simple. Some trucks disconnect the hot wire (pin 4) when they're not running, and some don't.
Rams probably don't is what i'm hearing.
Easy enough to check, just as you say.
And if pin 4 stays hot, I'll have to make other arrangements to isolate the truck battery when parked.
Until I figure out a way to automate that isolation, I guess I'll just unplug it when parked, then plug it back in when I hit the road again.

 

[BossHogg]

I'm missing something. Pin 4 on the four pin is the running light feed, on the seven-way, pin 4 is the electric brake feed.

Pin 1 is the battery feed on the 7 pin connector.

 

[9thousandfeet]

I'm missing something. Pin 4 on the four pin is the running light feed, on the seven-way, pin 4 is the electric brake feed.

Pin 1 is the battery feed on the 7 pin connector.

Oh boy. Our new truck is still on a train somewhere between here and Saltillo, so I can't go confirm it yet, but according to the pinout diagrams I've found on the internet, on the 7-way it goes like this.
pin 1 - ground
pin 2 - trailer brakes
pin 3 - running lights
pin 4 - battery charge
pin 5 - stop/left turn
pin 6 - stop/right turn
pin 7 - auxilliary/backup lights

is that not correct?

 

[Cardhu]

https://www.etrailer.com/question-363.html



the pinout is the same regardless of colours used.
https://www.etrailer.com/faq-wiring.aspx

 

[BWL]

Feels like everybody is over thinking this. Just unplug it when you're parked for the night. Not much harder than flipping a disconnect switch, which you could forget about as easily as forgetting to plug it back in when you start driving again and the free option. If you want to get fancy you could wire a relay into the hot wire and trigger it with an ignition wire so it only runs when the ignition is on.

 

[9thousandfeet]

The only problems with unplugging (this is not a towed camper, it's a slide-in bed camper) are that a)the plug is not the easiest thing to reach when the camper is fully loaded and tied down, and b) forgetting to plug it back in gives you no turn signals or brake lights.

An ignition-actuated relay would work for sure.

Another approach might be a voltage-sensing relay in the trailer harness hot wire that connects when it senses the voltage boost from the alternator, and disconnects when that voltage drops.
Seems to me that could even be installed in the camper instead of the truck , right before the hot wire goes into the camper converter.
That way I'd not have to mess with figuring out where on the truck to mount the relay and how/where to tap into the trailer harness.

Just have to find the right relay. I'm betting someone online knows, maybe here, or maybe on one of the camper forums.

 

[csuder99]

You probably want something like this: Battery Isolators | Battery Testers & Monitors | Battery Isolator Series
Basically what is used in motorhomes to isolate the vehicle battery from the the house batteries should work. Install it close to the converter as you said.

 

[BossHogg]

Oh boy. Our new truck is still on a train somewhere between here and Saltillo, so I can't go confirm it yet, but according to the pinout diagrams I've found on the internet, on the 7-way it goes like this.
pin 1 - ground
pin 2 - trailer brakes
pin 3 - running lights
pin 4 - battery charge
pin 5 - stop/left turn
pin 6 - stop/right turn
pin 7 - auxilliary/backup lights

is that not correct?

This is from my RAM owners' manual;

http://www.ramforum.com/images/styles/ram/attach/jpg.gif

Good news is the pin function versus its orientation is the same as eTrailer but the pin numbers are different. I don't know which pin numbers are correct, RAM's or eTrailer.

 

[BWL]

Now I see a simpler way. Waterproof relay on the battery power and run a jumper off the running lights to trigger it. Could even buy a short extension cord to run inline and wire the relay into it and only use it when plugged in. Rest of the time just leave it in a drawer or in the truck somewhere. Not sure how well I've explained this.

 

[BWL]

Figured I'd elaborate. Get a short extension cord for the 7 pin. On the cord cut the battery wire and wire 1 side to the source side of the relay and the other on the output. Do a 3 way splice on the cord off the ground and wire it to the relay ground terminal. 1 more 3 way on the running light wire tied to the trigger of the relay. Then clean up the wires with tape, zip ties etc and you have a removable battery disconnect you can use on any trailer with a 7 pin harness.

 

[9thousandfeet]

Good news is the pin function versus its orientation is the same as eTrailer but the pin numbers are different. I don't know which pin numbers are correct, RAM's or eTrailer.

That was both helpful and encouraging.
It would be a nightmare if there was not at least substantial agreement on how to wire up a 7-way trailer harness.
A uniformly accepted scheme for numbering the pins would be an advantage for sure, but so long as the positioning of the connections remains consistent it should all be good.
Thanks for that.

 

[PaulTGarrett]

I never could for the life of me understand why they made that big honkin' center pin connector the "aux/reverse lights" connector instead of making it the ground. Every pin on that connector references back to ground, why isn't it the biggest and best load carrying pin? Ah well... Just my random thought for the night...

 

[a12rag]

I have a 2002 Cummins that I tow the travel trailer with . . . I have left the trailer plugged in to the truck . . . I am sure that they have battery isolater to turn power off to the trailer when truck is not running . . . I think this is industry standard for a long time now . . . like having the plug for after market brake controller, built into the truck, instead of having to cut wires, etc. . . .

 

[crash68]

I am sure that they have battery isolater to turn power off to the trailer when truck is not running . . . I think this is industry standard for a long time now . . . like having the plug for after market brake controller, built into the truck, instead of having to cut wires, etc.

Nope. I know both a '14 2500 (with a factory 5th wheel prep) and a '15 1500 do not turn off the 12 volt battery power to the 7 pin plug. The pin stays hot whether the truck is running or not.
It's not to say the vehicle battery drain protection may turn it off(just like if you leave the lights on).