Tow Vehicle to Trailer Connections

[Capebuild]

Hello. I'm getting on to planning for all connections from the tow vehicle to the trailer. I'm a novice when it comes to auto electrical stuff like this so my questions are very basic.

I'm envisioning there's 3 "interactions" between vehicle and trailer:
1) Vehicle battery to trailer battery for charging battery on trailer.
2) Vehicle lights to trailer lights (brake lights, marker lights, turn signals, stuff like that)
3) Brakes. I'm planning on a Dexter axle with electronic brakes with proportional brake controller and possibly a parking brake for trailer (I realize probably not an "electrical" issue but a connection between auto and trailer).

Are all these connections done as 3 separate wiring runs? How do the connections occur (from auto to trailer). I've got a lot of reading to take in on all this, but I'm hoping some responses from the members here can get me pointed in the right direction as a place to start.

Thanks very much for any insights.

John

[Juneaudave]

John....If I remember correctly, your tow vehicle will be a Subaru Outback...Is that correct? And does it already have wiring for a flat 4 plug?

[Capebuild]

Hi Juneaudave, you have a good memory :-)
Yes, 2019 Subaru Outback and I do have a hitch installed with 4 pin wiring. I pull a boat trailer so that connector does illuminate the lights on the boat trailer.
So I'm assuming I can gather the wiring for the brake lights, turn signals, marker lights on the trailer, terminate those in a corresponding 4 pin connector and attach
to 4 pin connector coming off Subaru and that makes the connection for the lights on the trailer.

I'm assuming, again, there needs to be some other wiring connection to accomplish battery to battery charging, as well as the brake connection... ??

thanks.
John

[Sparksalot]

You will need the 7 pin round connector. Everything you described happens in that. I bet if you looked at e-trailer.com they have a kit to upgrade your TV.

[Socal Tom]

See if there is a factory harness available for a 7 pin connector. If not you probably want something like this

https://www.etrailer.com/Wiring/Tow-Ready/30717.html

[Capebuild]

Thanks a lot for those tips, Socia Tom and Sparksalot. I looked up that product from the link you posted. Watched a video shown on the Etrailer site. Very helpful. They have this product shown in the attached photo. This makes sense and seems like what I'm looking for. Kind of makes it easy, I think. This 4 way to 7 way pin connector seems to take into account the brakes, the lights and the battery to battery charger. Need to study it a bit more, but I think this is the solution.

Thanks again.

John

[TimC]

Curt and maybe other mfrs make a vehicle end that incorporates both the 7 way and 4 flat connector in one unit eliminating the need for an adapter to pull your boat trailer. Etrailer is very helpful if you talk to or chat online with them. They'll point you at exactly what you need.

Similar to this...
https://www.etrailer.com/p-C55774.html?hhyear=2019&hhmake=Subaru&hhmodel=Outback+Wagon

Good luck. Tim

[swoody126]

Thanks a lot for those tips, Socia Tom and Sparksalot. I looked up that product from the link you posted. Watched a video shown on the Etrailer site. Very helpful. They have this product shown in the attached photo. This makes sense and seems like what I'm looking for. Kind of makes it easy, I think. This 4 way to 7 way pin connector seems to take into account the brakes, the lights and the battery to battery charger. Need to study it a bit more, but I think this is the solution.

Thanks again.

John

Capebuild, the image you are showing is the trailer side

the 4-prong flat plug has 3 unshielded male prongs which if they were on the TV could short out when the different lights were activated

here are a couple images that may help some

12d67469d97e8788cf42e7c0e54434df.jpg (14.75 KiB) Viewed 1278 times

trailer-wiring-color-code-diagram-l-f3629d12b232a3b1.png (124.61 KiB) Viewed 1278 times

BON CHANCE

sw

[John61CT]

The charging of a deep cycling House battery in the trailer

from the alternator of the TV

is not so straightforward.

The amps current flow might be as high as 50-60A

requires a separate fat wiring pair and Anderson connectors

and likely a DCDC charger like Sterling BB series to counteract the voltage drop over distance.

[featherliteCT1]

what John61CT said +++++++

[Capebuild]

Thank you all again for the follow up and suggestions. I really need to wrap my head around all of this as it's all pretty much unfamiliar territory for me. But with these illustrations you've posted I can do my research and get a bit more knowledgeable with what I'll need. I have been looking at a set up another person had posted on youtube which really spelled out everything pretty clearly. It had a lot of components but it all seems to makes sense. He had a Sterling battery to battery unit in the mix (photo attached). His set up took Solar, batt to batt charging and shore power into account. I'm just pretty unfamiliar with the connections needed between tow vehicle and trailer... so will study up. I'll post the youtube schematic I had seen which I've been studying.

Thank you all again, I appreciate it.

Actually, one other question, Swoody, the diagram you posted, shows a red marker light at the rear of the trailer and an amber in the front. Is there a reason one is red, the other amber?
I just found that diagram on line, as well, from Johnson Trailer Parts with a good article on wiring. Thanks

John

[Tom&Shelly]

...The amps current flow might be as high as 50-60A ...

Exactly how big of a fuse do you put in that circuit?

I think most of us who are charging from the TV alternator are looking for about 10 amps max, so 10 gauge wire, through the 7 pin connector, and 30 amp fuses are fine. If a 100 Ah battery is half discharged (as discharged as you'd want to be with lead-acid or AGM), that's about 5 hours of driving to recharge it.

See the 2nd post on this thread: http://www.tnttt.com/viewtopic.php?f=30&t=28620

Tom

[featherliteCT1]

The Sterling DC to DC charger says 30 amps. So, that 200 ampH battery shown could easily accept 30 amps. Given the long distance between the alternator and the trailer battery, I would use a plenty big wire determined by one of the AWG calculators online. My preference is to use the Renogy calculator on their web page. Once the AWG is determined, size the breaker 125% more than what is called for. Remember, we are protecting the wire not the devices.

I ran 3AWG equivalent copper wire from my 2018 Silverado truck battery back to my trailer battery (total distance for me is about 35 feet). I hate voltage drop and did not want to damage my alternator.

Also, make sure the vehicle's alternator can handle the load. Most alternators can be expected to provide continuously about 1/2 the maximum rated output power -- possibly as much as 2/3 for a conventional "heavy duty" design. Otherwise, the diodes in the alternator can overheat and burn out ... at least on my 145 ampH alternator.

Others may have different opinions.

[Socal Tom]

Thanks a lot for those tips, Socia Tom and Sparksalot. I looked up that product from the link you posted. Watched a video shown on the Etrailer site. Very helpful. They have this product shown in the attached photo. This makes sense and seems like what I'm looking for. Kind of makes it easy, I think. This 4 way to 7 way pin connector seems to take into account the brakes, the lights and the battery to battery charger. Need to study it a bit more, but I think this is the solution.

Thanks again.

John

Capebuild, the image you are showing is the trailer side

the 4-prong flat plug has 3 unshielded male prongs which if they were on the TV could short out when the different lights were activated

here are a couple images that may help some

12d67469d97e8788cf42e7c0e54434df.jpg

trailer-wiring-color-code-diagram-l-f3629d12b232a3b1.png

BON CHANCE

sw

No, he has the right thing. It plugs into the TV and adapts the 4 way to a 7 way.

[Socal Tom]

Why do you guys have to make everything so complicated?

The adapter you found is perfect for converting the TV 4 way to a 7 way with trailer brakes. Just run a 30 amp circuit breaker with a 12 guage wire. If it pulls 50 amps something is wrong. I’ve been running a factory jeep harness for years with less than 12 guage, its fine, and it was designed at the factory and its behind a 200 amp alternator, its fine.
Don’t worry about fancy dc/dc charging unless your have lithium batteries or are a millionaire, or have a desire to waste money.

KISS is good engineering practice, it means Keep It Simple Stupid. It gets forgotten on a lot of sites like this. If your a weekend warrior like me and you don’t want a gold plated trailer you use a few times a year, then take my advice.