Charge Line

You are correct Mapguy, I no longer have my 2006 and was going from memory on the fuse size. Regardless, if he doesn't have a fuse in that location, it will not charge the batteries. Have found several people that didn't know that.

I was reading the manual on my new truck and it says to improve charging, one can turn the truck lights on.

Left my old truck and trailer at a axle shop to have the axles aligned for a few days. Cable was hooked up during that time and drained the truck batteries. Required a jump start.

Charlie D. wrote:
Is this a new problem? The 2006 D/A did NOT come with a fuse installed to charge the batteries. 50 amp fuse is needed. Perhaps it is blown if it is a new problem. Pull the fuse panel cover on the drivers side under the hood above the tire. IIRC, it is the second slot from the top left. About 1/2" square.

It is critical that the battery is charged because it engages the brakes in the event of a trailer disconnect.

Actually a 40 Amp fuse in the UBEC (underhood fuse panel) to protect Stud 1 output to the RV 7 way trailer plug terminal 4.

My truck is same as OP except extended cab and it charges the 4x6v batteries in my toyhauler fairly quickly driving on the way home from a camping trip. Performance can be improved by installing larger wire but that may load the Alternator too much for reliability.

The GM wiring scheme does put the truck starting batteries at risk of discharge when camping if the RV 7 way is left connected to the truck. I always disconnect unless overnighting in a parking lot or rest area.

Thanks to all who replied. I think I have created a non-issue. I'm not going to worry about it.

Is this a new problem? The 2006 D/A did NOT come with a fuse installed to charge the batteries. 50 amp fuse is needed. Perhaps it is blown if it is a new problem. Pull the fuse panel cover on the drivers side under the hood above the tire. IIRC, it is the second slot from the top left. About 1/2" square.

It is critical that the battery is charged because it engages the brakes in the event of a trailer disconnect.

Don't forget a large enough alternator if you want 100 amps to trailer.

The truck in stock configuration will charge the batteries. The question is how much and how fast. Installing larger wire from you're truck's batteries back to the 7 pin plug will help greatly. #8 is about the largest that will fit in the connection on the 7 pin plug. However, you can run larger wire and splice it to a short piece of #8 right at the plug.
Some people have installed a separate cord, just for the + and - wires, to run really heavy wire. I think one made for lift gates on big rigs takes up to a #2 wire for 100 amps. Of course, the wiring on the RV side of the connection would also need to be upgraded.
I would install at least a #8 (properly fused at 50 amps) from your truck battery back to the 7 pin plug and hook it to the +12v terminal in place of the factory wire. If you would like to have this wire unhooked when the truck engine is off a voltage sensing relay (Blue Sea makes a good one) will be needed.

I have experienced dead batteries while boondocking and all I did was hook it to truck for awhile and all was good. I have never had a problem with the truck not charging the couch battery on 3 different units with 3 different trucks since '82. Just something I did not worry about.

Here is the way I am planning on attacking this problem... This is using a SMART RELAY made by a couple of companies in particular by BLUE SEA. The one I am interested in is the Blue Sea model SI-Series PN 7610/7650

Here is my planned diagram for using this ACR relay with my 2010 F150 Truck Alternator system


please read up on the ACR relay operation from the BLUE SEA site...
BLUE SEA ACR RELAY 7610


The only downside I see may be whether or not the 2010 F150 Alternator charging system is rated enough to handle the additional batteries in the system. It may go up in blue smoke for all I know... This is something you will need to think about before adding additional batteries to any alternator charging system.

My system is required to provide me with a separate battery bank located in the back of my truck bed that will support my heavy use of two way radio equipment when in my truck only on COMM ALERTS as well as providing extra batteries for use with my OFF-ROAD POPUP camper when in camping mode. I will have Trojan T1275P 300AH Capacity batteries in both locations that can be paralleled when in camping mode to give me 600AH total capacity.

Using the BLUE ACR relay will not ever let my truck start battery to get discharged which is rule number one to don't mess with your truck otherwise you won't have a horse to get back home on. The BLUE SEA ACR smart relay concept is it parallels (combines) batteries during charging, and isolates them when charging has stopped and after battery voltage has fallen. An ACR is intended to keep a load from discharging both of the batteries. The ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR's contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries.

In my case I will be using both battery banks connected together for the most part which will be isolated from the truck electronics completely using BLUE SEA four position battery switches and both banks will be normally re-charged from the RV Trailer side using a 2KW Honda generator and the trailer on-board PD9260C converter/charger unit.

The time I will be using the 300AH batteries for operating just my two way radios from the truck alone I hopefully can have them re-charged from the truck charging system. I will have my 2KW Honda Generator which is always securely mounted in the bed of my truck which could operate a 120VAc B&D VEC1093DBD 40 AMP smart mode battery charger to re-charge my 300AH battery setup when needed and not depend on the truck alternator at all.

This is my OFF-ROAD POPUP trailer layout showing where all of battery systems components are located.


Just passing all of this along as it could fit your requirement somewhat if and I emphasize "IF" the truck alternator charging system is rated high enough to charge a bank of 300AH batteries without burning out the truck alternator system...

Food for thought
Roy Ken

You may want to measure the charge current before you change anything. Pull fuse in the cgarge line & put an ammeter acros it. I never had any problems charging the batteries in my 5er. When I boone docked for several days just plugging into the truck for an hour or so didn't help much. I would use jumper cables, start my truck & they charged quickly.

When we lived on Long Island we boondocked at the beach all the time and never had a problem with truck charging batts. We would hook truck to trailer and let it run a few hrs. when batts were low.