7 Way charge Line Saga

[ATskier]

I thought others who are considering using the factory charge line that runs into a seven way trailer bumper hitch plug might be interested in this story.

I have a ’06 Duramax with factory trailer wiring.

I’ve had four campers on this truck, all using the factory charge line to the bumper for battery charging. One camper was installed at the factory, where the owner said no problem to use factory hitch charge line; they used a line off the back of the pop up, to the bumper socket.

Currently I have a canopy on my truck and some lighting and other little stuff (<3amps, yes I'm sure!) pulling on that charge line. Well I started to see flickering lights. I saw voltage all over the place, but eventually stabilizing at 12.7 volts. When I tried to draw more than an amp out of the charge line, voltage would drop below 10 volts.

I concluded connectors or 7 way plug or Y to bed mount plug were bad. Well I tested all that and they were fine. So my issue was in the factory wiring. I was surprised to see this line is protected by one 60 amp fuse… but the gauge is not close to 60 amp, though still maybe a 12 gauge. Plenty to send a few amps back to the camper or canopy.

I took truck to dealer explained situation…they punted. They could only test voltage with no load at the bumper. Said it was fine. They could not tell me how many amps you might reasonably draw off the 7-way charge line.

So I concluded at one point or another I probably pulled a lot of amps through that charge line to try to charge a couple of deeply discharged battery's in a camper…a very common situation…and burned up the charge line. Note I checked the grounding. It was fine.

I clipped the charge line into the bed mount and ran an new 8 gauge wire protected by a 30 amp fuse from the alternator to that plug. It took longer than I would have thought. Things working now.

I concluded Lance was right. Do not use factory charge line or even seven way plug for any kind of serious amp draw.

Any thoughts?

 

[Betarocker]

The charge circuit is only for keeping the batteries topped up. The size of the wire and the fuse are only for low current applications. I ran into the problem with a dumping trailer that had a low battery. If I towed that trailer more often, I'd run a fused heavy gauge cable pair from the truck's battery and have a quick connect jumper cable type connection to the trailer battery. Now I just plug in the charger the day before I think I'll need the trailer.

 

[Martyn]

I’d agree with pulling a dedicated line for charging the camper, 10 gauge is standard some people pull 4 gauge for heavy duty and fast charging.

Regarding your original issue, if you know the gauge of the stock wire running to the 7 pin and it’s length you can calculate the resistance of the wire and then check the actual resistance with a meter. If the resistance is higher than anticipated then the problem is with the wire itself.

 

[ATskier]

I thought about the resistance check but leads on multimeter were too short. I was hoping Chevy dealer would do something like that but they just checked voltage.

 

[DaveInDenver]

Pull the fuse and short the charge pin to the ground at the 7-pin connector. Measure resistance of the conductor side empty fuse socket to ground or frame. Shouldn't need long leads for this.

Sounds to me like you have dodgy connections, corrosion, broken wires. I'm betting there's 3M Scotchlok T-taps involved somewhere.

 

[ATskier]

Thanks for both responses.
I suspect a lot of people are using a similar setup to what I have to charge camper batteries. The widely sold bed plug harnesses tie right into factory charge line.

Amazon.com: CURT 56070 7-Foot Vehicle-Side Truck Bed 7-Pin Trailer Wiring Harness Extension for Select Chevrolet, Dodge, Ford, GMC and Nissan Trucks: Automotive

Buy CURT 56070 7-Foot Vehicle-Side Truck Bed 7-Pin Trailer Wiring Harness Extension for Select Chevrolet, Dodge, Ford, GMC and Nissan Trucks: Wiring Harnesses - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[ATskier]

So I solved my problem by putting in the new line.

I do suspect corrosion broken wiring somewhere but prob easier to replace than fix that line.

I still question if new factory 7 way wiring is adequate to charge camper batteries.

 

[ITTOG]

I still question if new factory 7 way wiring is adequate to charge camper batteries.

Yes if you are just charging to maintain. If you have a dead battery or low battery it will not. If you are not careful it could melt the shielding and start a fire.

 

[ATskier]

Yes if you are just charging to maintain. If you have a dead battery or low battery it will not. If you are not careful it could melt the shielding and start a fire.

I could see that happening given a 60 amp fuse and a 10 or 12 gauge wire.

 

[Bayou Boy]

So I solved my problem by putting in the new line.

I do suspect corrosion broken wiring somewhere but prob easier to replace than fix that line.

I still question if new factory 7 way wiring is adequate to charge camper batteries.

No. It’s not. I have a brand new Ram 3500 and my Victron shows all of 3 amps flowing through the 7 way when my batteries are discharged. I bought a 6/2 marine duplex cable and an Anderson plug but haven’t installed it yet. However, a quick temporary test showed 35-40 amps flowing at idle with that cable.


Sent from my iPhone using Tapatalk

 

[ITTOG]

It won't take anywhere near that much, especially if there was any corrosion in the wire.

A quick search indicated
For a 12-volt system, 10 AWG wire safely conducts up to 20 amps for 15 feet or up to 5 amps for 70 feet

 

[Bayou Boy]

It won't take anywhere near that much, especially if there was any corrosion in the wire.

A quick search indicated
For a 12-volt system, 10 AWG wire safely conducts up to 20 amps for 15 feet or up to 5 amps for 70 feet

Exactly. And you won’t see close to that with all of the connections in the mix.

The positive connection on the 7 way is solely to keep the electric brake battery topped off enough to stop the trailer in an emergency. That’s it. Don’t expect anything else.


Sent from my iPhone using Tapatalk

 

[Justin Cook]

Worth noting in here that DC cable length calculations have to be round-trip... so, yes, 10AWG wire safely conducts up to 20A for 15', but that's round-trip, meaning 7.5' on the POS leg + 7.5' on the NEG leg, not 15' from the charge source (which would be 30' round-trip).

 

[Bayou Boy]

Worth noting in here that DC cable length calculations have to be round-trip... so, yes, 10AWG wire safely conducts up to 20A for 15', but that's round-trip, meaning 7.5' on the POS leg + 7.5' on the NEG leg, not 15' from the charge source (which would be 30' round-trip).

And on all but the smallest vehicle/trailer combos the real distance is more like 60-70ft round trip.


Sent from my iPhone using Tapatalk