Breakaway Battery Charging

[Scrounger]

I wanted to start a new thread to get some details on this one. I have a 2000 Yukon XL with a brake controller installed. When I leave my trailer plugged in for a few days, it will drain my trucks battery to nothing. I've read in several posts that the battery is not supposed to charge unless the truck is keyed on.

That is not the way my truck is working.

How can I test to see that it is charging while the key is off.

 

[kennyd]

Does your brake controller indicate that is has continuity with the trailer? If so that could cause the draw down of your battery.

To check the charging ability while the key is off, you will need a voltmeter to check the 12v pin of your trailer plug.

 

[RobertN]

All the factory charge lines I have seen have power to the trailer plug all the time. You have to add an isolator; that will only allow power to the charge line, when the vehicle is on.

 

[kennyd]

All the factory charge lines I have seen have power to the trailer plug all the time. You have to add an isolator; that will only allow power to the charge line, when the vehicle is on.

My '92 F250 does not, there is a relay that only allows 12v to the plug when the key is is the RUN position...pretty sure all the newer vehicles are setup that way-especially if they have the "trailer towing" option.

 

[BOBBYROGERS]

all the systems i have seen that charge the break away battery off of your truck have a led light on them to let you know that they are charging you may want to look at yours and see it .would let you know pretty quick if yours is constently drawing power when the key is off

 

[George2615]

Attached is trailer plug info for 7, 6, and 4 pin wiring.

On the 7 pin plug Pin 4 is 12 V hot from the vehicle. On GM trucks this lead comes from the fuse box under the hood and is the charge lead that feeds the trailer battery. It has battery voltage at all times and does not go through the brake controller.

Pin 2 is the blue lead from the brake controller. It should only have voltage on it when the vehicle brakes are applied.

Turn signals and running light pins (5,6,&3) also do not have power unless they are operated with the ignition key on.

Pin 7 backup light pin should not have voltage unless the ignition key is on and truck is in reverse.

Of course the ground (pin 1) should not have voltage.

If your trailer is plugged into the truck plug the ONLY PIN that should have voltage is pin 4 (the 12v charge lead). If there is voltage on the other leads there is a problem with the controller. Your trailer battery may be draining the truck when left plugged in.

When leaving your trailer hooked up for several days and you are not going to use the truck it would be best to unplug the trailer and put a note or tag on the steering wheel reminding you to plug it back in before use.

I have an 07 GM 2500HD and this wiring explanation has been correct for GM's as far back as I can recall.

 

[Diamondpilot]

All the factory charge lines I have seen have power to the trailer plug all the time. You have to add an isolator; that will only allow power to the charge line, when the vehicle is on.

I have to disagree with you on that one. I sell boats and trailers on the side and have wired over 25 vehicles since the first of the year and have seen none that were hot with the key off. I deal with 75% Fords and the rest are GM with a few Nissans, Toyota's, and Jeeps but very few Dodges.

Chris

 

[Diamondpilot]

My '92 F250 does not, there is a relay that only allows 12v to the plug when the key is is the RUN position...pretty sure all the newer vehicles are setup that way-especially if they have the "trailer towing" option.

You are correct Kenny. That is the way it should be.

Chris

 

[Scrounger]

all the systems i have seen that charge the break away battery off of your truck have a led light on them to let you know that they are charging you may want to look at yours and see it .would let you know pretty quick if yours is constently drawing power when the key is off

No idea where the LED would be. On the truck or the trailer. Nothing on the trailer that I can see. This is a mystery to me. Maybe I should call a GM service line if I can find one.

 

[RobertN]

I have to disagree with you on that one. I sell boats and trailers on the side and have wired over 25 vehicles since the first of the year and have seen none that were hot with the key off. I deal with 75% Fords and the rest are GM with a few Nissans, Toyota's, and Jeeps but very few Dodges.

Chris

My exposure has been, very limited in that arena. For my Dodge, I got an isolator when I went to put the camper on.