Batteries NOT charging while towing

[Splashers3]

Did a search and saw some good info about batteries charging/not charging while towing...but here's a situation some may not know about - I didn't, and I've towed for nearly 6 yrs with my 2008 2500 D/A.

Picked up trailer from RV repair shop (yearly maintenance), battery in trailer too weak to raise landing gear. They suggested plugging cord into truck' 7-pin outlet, which SHOULD have supplied power to raise gear. Well, it did NOT. They got a battery and jumper cabled it in, and the gear raised. BUT there is much more to this story.

Tech checked for 12v - nothing. Nothing in bed outlet, nothing at bumper outlet. Checked fuse box, 30A fuse present. Tech starts peeling away wrappings on one of the cable runs...pulls out a wire and hooks up to fuse box post next to break controller.

Guess what, 12 volts supplied to both outlets! He said this happens all the time, by all the truck manufacturers - even though I had the towing package option. They fail to hook this wire up....so for 6 yrs I NEVER had 12 volts charging battery while towing...since we always hook up to shore power the battery drain was never noticed.

We will continue using Affordable RV & Truck Repair in King George, Va....that was a bonus - and they didn't charge!

I hope this will cause folks to check their TV - there are probably several folks in this boat, and don't know it.

[2500_Grunt]

Bobbo wrote:
I love this tester. You know exactly what you have, including 12v hot wire. Shows RT (right turn) TM (tail/marker) LT (left turn) 12v BK (brake) and BU (backup).

4 pin/7 pin tester.

That along with a zip lock bag full of fuses should be in every glove box. Also add a 12v probe/tested.

[webecreekin]

S3, these General Motors trucks have a fuse/relay that is the underhood fuse box, that is required to charge the batteries while hooked up. Mine had it installed as part of the towing package with the harness. Some trucks in the club have been delivered without them. Take a look at it from that point-of-view.

[ianmac23]

Not sure if it is true or not but they told me for GM the 12v is a dealer installed option. They "normally" charge $100 for it

[Splashers3]

that is very similar to what the tech used to ID there wasn't voltage...I am in the process of getting one of those....darn handy inexpensive instrument.

Something to add to everybody's toolbox...along with one of those 30Amp female fuses that protect the 7 pin circuitry.

[Bobbo]

I love this tester. You know exactly what you have, including 12v hot wire. Shows RT (right turn) TM (tail/marker) LT (left turn) 12v BK (brake) and BU (backup).

4 pin/7 pin tester.

[rhagfo]

Splashers3 wrote:
Did a search and saw some good info about batteries charging/not charging while towing...but here's a situation some may not know about - I didn't, and I've towed for nearly 6 yrs with my 2008 2500 D/A.

Picked up trailer from RV repair shop (yearly maintenance), battery in trailer too weak to raise landing gear. They suggested plugging cord into truck' 7-pin outlet, which SHOULD have supplied power to raise gear. Well, it did NOT. They got a battery and jumper cabled it in, and the gear raised. BUT there is much more to this story.

Tech checked for 12v - nothing. Nothing in bed outlet, nothing at bumper outlet. Checked fuse box, 30A fuse present. Tech starts peeling away wrappings on one of the cable runs...pulls out a wire and hooks up to fuse box post next to break controller.

Guess what, 12 volts supplied to both outlets! He said this happens all the time, by all the truck manufacturers - even though I had the towing package option. They fail to hook this wire up....so for 6 yrs I NEVER had 12 volts charging battery while towing...since we always hook up to shore power the battery drain was never noticed.

We will continue using Affordable RV & Truck Repair in King George, Va....that was a bonus - and they didn't charge!

I hope this will cause folks to check their TV - there are probably several folks in this boat, and don't know it.

This a a very good dealership!!!
Some bill for every minute they work on your rig. Others realize there is far more profit doing "Free" work. It is a habit of the better shops, when they do charge for work the price is fair for the work done, and the quality is there also.

[Old_Days]

Owning a truck camper I wanted a second battery so after a lot of help from this forum and others decided to go with dual battery's with isolator under the hood,then I hooked up the 7 pin plug wire to second battery with a breaker,so I can stop power to TC when I want.

[trop-a-cal]

I may be a liability problem with codes in the state unit is built. Dealer may have also been told it was not connected or they too were under a code which they could not comply with. So liability is then shifted to the one that hooks it up, if in fact it is not to code. More research should be done to confirm if it is after hooked up a safe system, as they may have not done the required work by "general code" which should be the highest code in the country, as only then does it meet the design safety for the industry.

[Old_Days]

On my 2007 GMC I had to buy a fuse and a 6 milometer nut to hook up the 7 pin plug,nothing in the manual learned about it on a GMC truck forum.

[RoyB]

My 2004 Ford F150 charged my batteries when connected to the 7-way trailer connector. When I got my 2010 Ford F150 which came with tow package I right away noticed I was not seeing a rise in DC VOLTAGE at my battery terminals with the 2010 F150 truck running.

Further checking I found an unmarked package in the truck glove box with a RELAY and a FUSE in it. Checking the manual I see the FUSE PANEL mounted on top of the radiator under the hood has tow positions identified in the manual as TOW CHARGE or something like that and was missing a RELAY and FUSE.

Installed the two parts and fixed my problem for not charging the trailer batteries when connected to the 7-way trailer connector.

Installing the RELAY and FUSE allows my truck to charge the trailer batteries when the truck ignition key is TURNED ON. I like this feature as this will keep the trailer from running down the truck start battery if left connected to the 7-way trailer connector without the truck running.

I guess one must be aware of things like this on their own as nothing was passed on about the unmarked FUSE and RELAY package in the glove box by the dealership.

Roy Ken