Charging truck via 7 pin trailer wiring

hoitzed · May 3, 2022

I understand there is a 30A rated always on connection at the 7pin trailer connector. Is there a diode or other reason why I shouldn't / couldn't put a trickle charger through the 7pin to charge my battery? I have limitations on how I park and where electrical outlets are available, and would rather not drag an extension to the front of the truck all the time.

Thanks

CaryBosse · May 3, 2022

I would double check the Outfitter Guide for the 2017, but I do not see a diode or anything that would actually prevent what you are considering on the 2015 wiring.

To aid in your search, I think the fuse F24UA would be a good search term.

Whiteec1 · May 3, 2022

Hello,

See link for a product that might work with this situation. You might wish to call this manufacturer and see if this could be a solution for charging.

RVGUARD 7 Way 8 Feet Trailer Cord with 7 Gang Junction Box Kit,Include 12V Breakaway Switch and Plug Holder, Trailer Connector Cable Wiring Harness with Waterproof Junction Box

TRUCK BED EXTENSION:This trailer wiring harness is designed to be an extension of the existing tow wiring of your truck, plugging into a 7-way RV blade socket for connecting 5th wheel wiring or gooseneck wiring. SIMPLIFY CONNECTION:Heavy duty 7-way molded plug with premium double prong provides...

rvguardstore.com

ARCowboy · May 4, 2022

Hm... I don't see any reason why you couldn't, but I don't think you should... or rather I would not use the 7 pin like that.

Alternatively, you could run a 25' battery tender extension along your frame to the rear ?

If you have any bigger power needs from the rear of the truck (Not sure what you use your truck for, but if you want to run a winch from the hitch or similar high amp draw) you could run some thick 1/0AWG or 4AWG and an Anderson Power Pole connector for a lot of versatility including charging

ajp · May 4, 2022

CaryBosse said:
I would double check the Outfitter Guide for the 2017, but I do not see a diode or anything that would actually prevent what you are considering on the 2015 wiring.

To aid in your search, I think the fuse F24UA would be a good search term.

I see the same thing for a 2021. F24UA (30A fuse) is in the engine fuse block which is powered from a 250A fuse (V6 gas engine) at the battery. It appears it is the orange wire used for +12V auxiliary power at the trailer plug, or the taped up harness under the bed for adding the plug.

A lot of circuits are interconnected to that fuse, so I would be sure you are connecting a reliable, clean voltage not to exceed 15VDC, and fuse it much lower than 30A.

hoitzed · May 4, 2022

Thanks for the responses! I currently use the charger connected to the battery / grounding post while it's still connected to the vehicle, nothing blew up yet. The voltages are pretty stable if it's not in repair mode.

Tom S. · May 4, 2022

I would be more inclined to wire up a direct battery connect and either mound a plug into the front fascia or through the grill. I did that with my zero turn lawn mower so it's simple to plug and unplug between uses. Got these from Amazon:

Cut the wire in half and wired the female plug to the battery and the male plug to the tender.

littleblazer · May 4, 2022

Any car I have that gets a tender uses the cigarette/12v receptacle plug. I hate clutter. In this case it should work, however I could see there being some voltage drop issues across the run. I've seen chargers do some weird things when not hooked up at or near the battery....

Tom S. · May 4, 2022

littleblazer said:
Any car I have that gets a tender uses the cigarette/12v receptacle plug. I hate clutter. In this case it should work, however I could see there being some voltage drop issues across the run. I've seen chargers do some weird things when not hooked up at or near the battery....

Some cars kill that connection a few minutes after the ignition is turned off to prevent battery draw from third party equipment like radar detectors. I believe my Colorado does.

littleblazer · May 4, 2022

Tom S. said:
Some cars kill that connection a few minutes after the ignition is turned off to prevent battery draw from third party equipment like radar detectors. I believe my Colorado does.

I moved the fuse over to the other slot so that doesn't happen in mine. But yes, that is true they come that way. I leave too many things plugged in and charging at stops for that to go off anytime the key is out.

CaryBosse · May 4, 2022

My thoughts, randomly from the comments.

The OP is looking for a battery tender, I tend to think this is minimal current draw. That said, I am not sure how the tender will react to what may be a large voltage drop across the length of the wiring. However, a wire designed to handle 30 Amps, with a battery tender probably putting out 1-5 amps max, should not be an issue I would think.

One comment was regarding a battery tender that plugs into a cigarette lighter. The cigarette lighter circuit on our trucks is protected by a 15 amp fuse, so that setup is likely to have lighter wire and a still works, as designed.

The OP is trying to avoid running an extension cord to the front of the truck. Some of the suggestions to setup a wire run to the back of the truck would help, but he is trying to avoid any of that I would assume.

I do not see anything that suggests that Fuse F24UA has anything in the circuit that would shut it down at any point. This of course means, from a trailering standpoint, if you leave your travel trailer plugged in with any current draw, you are going to kill your battery if the engine is not running.

My memory when I setup and checked out my trailer brake controller on my 2015 Canyon was that there was always 12 volts on the 7 pin.
My belief is my Silverado also always has power. I haven't checked that out, but it seemed like it was the case. I never leave my travel trailer plugged in with the engine not running for long periods. Also, I have used the truck power to operate the tongue jack without the battery switch on the trailer in the ON position.
Based on what I have heard, this is not true for all trucks, Ford and Ram may kill this power.

Finally, I purchased one of these for my Silverado. My goal was to allow me to have a 12 volt output at the rear of the truck, so I could use a portable air compressor to fill up my travel trailer tires. So far, I have not needed it, so no clue how well it will work. It would seem it would make for a very clean installation of a cigarette lighter style battery tender into the 7 pin connector.

https://www.4wheelparts.com//p/tow-ready-7-way-to-cigarette-lighter-plug-adapter-118019/_/R-DJSK-118019

153537 · May 4, 2022

Tom S. said:
Some cars kill that connection a few minutes after the ignition is turned off to prevent battery draw from third party equipment like radar detectors. I believe my Colorado does.

True, but that can be changed by moving the fuse position (search on here for always on cigarette lighter port).

CaryBosse · May 4, 2022

That fuse swap only applies to the cigarette light outlets, not the 7-pin 12 volt auxiliary power.

153537 · May 5, 2022

CaryBosse said:
That fuse swap only applies to the cigarette light outlets, not the 7-pin 12 volt auxiliary power.

Correct. The post I was responding to was referring to the cigarette lighter outlet only.

Chuck_B · May 5, 2022

The 7-pin would work fine for a trickle or maintenance charger. I currently use the cig lighter outlet in the console (after moving the fuse).
The garage has outlets in both locations and the trailer plug would actually be more convenient. I think I'll switch setups. Thanks for the post @hoitzed .
I already have the compressor I keep under the back seat wired to a trailer connector. It's nice not having to pop the hood for that.

hoitzed · May 5, 2022

I've got a compressor that plugs into the trailer connector too. Thanks for all the suggestions, the cigarette lighter port wouldn't work for me, I wouldn't want to leave my door ajar all night with a cord hanging out. I have considered running something more substantial to the rear of the vehicle for stuff in the future (eg. dc-dc charger or inverter); hard to source anderson connectors in Canada though. Time to buy more trailer connectors!

C21964 · May 5, 2022

If I leave my trailer connected (which has 2 onboard 12v batteries) I can still run my truck battery down eventually by running with a load on the accessory position. I have done this when using the truck WiFi for extended periods. So this makes me think it is a "one way" diode equivalent connection that allows the truck to slowly (current limited) charge the RV batteries when running, but not the reverse.

Personally I think post #7 would be the cleanest and easiest way to do what you want.

CaryBosse · May 5, 2022

C21964 said:
If I leave my trailer connected (which has 2 onboard 12v batteries) I can still run my truck battery down eventually by running with a load on the accessory position. I have done this when using the truck WiFi for extended periods. So this makes me think it is a "one way" diode equivalent connection that allows the truck to slowly (current limited) charge the RV batteries when running, but not the reverse.

Personally I think post #7 would be the cleanest and easiest way to do what you want.

But is the diode on the truck or the trailer? The truck wiring diagram doesn't show a diode.

Trying to think of a way to check this out, but I would have to go by one of those cigarette lighter trickle charger.

littleblazer · May 5, 2022

CaryBosse said:
But is the diode on the truck or the trailer? The truck wiring diagram doesn't show a diode.

Trying to think of a way to check this out, but I would have to go by one of those cigarette lighter trickle charger.

Put a meter on it with a diode checker, at least on my 2019 colorado it passes no diode both directions from positive at the plug to the battery... just tested.

CaryBosse · May 6, 2022

littleblazer said:
Put a meter on it with a diode checker, at least on my 2019 colorado it passes no diode both directions from positive at the plug to the battery... just tested.

Thanks, saved me the trouble.

I suspect the trailer that @C21964 was talking about has some sort of diode protection so the batteries on the trailer do not get drained.

Charging truck via 7 pin trailer wiring

hoitzed

CaryBosse

Whiteec1

RVGUARD 7 Way 8 Feet Trailer Cord with 7 Gang Junction Box Kit,Include 12V Breakaway Switch and Plug Holder, Trailer Connector Cable Wiring Harness with Waterproof Junction Box

ARCowboy

ajp

hoitzed

Tom S.

littleblazer

Tom S.

littleblazer

CaryBosse

153537

CaryBosse

153537

Chuck_B

hoitzed

C21964

CaryBosse

littleblazer

CaryBosse

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