Trailer tow wiring for the 2013 and 14 trucks

[Kirwin]

I have been researching what could go wrong if you connect a trailer with a dead short or some other wiring problem to my 2013 Ram as I am familiar with the TIPM issues we went through a few years back. So after much research as best as I can tell the Body Control Module (BCM) located in the left side kick panel is now the brains of the system and controls all lighting functions much the same as the old Front Control Module (FCM) or TIPM. The headlights have a discreet wire dedicated from the BCM to each filament. So the BCM powers them directly via a driver circuit. If there is a relay involved I can't find it, nor is it described in the service manual. The taillights and rear brake lights and backup lights seem to have this same set up: a wire from the BCM to each filament with a common ground for the assembly. Keep in mind that the high end taillights are now LED so they draw very little power. The backup lights remain a 921 lamp and the marker light and license lights are still 194s. All of this is well within the power limitations of the BCM. I still think that the headlights themselves are a little high on the list of things that would be better served by a relay but apparently that is not the design they used. There are several fail safes built in so that the headlights remain on on low beam if the communications buss were to fail or lose connectivity.
This brings us to the trailer circuits. There are 4 relays in the Power Distribution Canter (PDC) on the PDC PC board as best as I can tell since they are not any of the relays you see when you remove the PDC cover. One for trailer tow backup lights via fuse F-27, one for trailer tow tail lights via fuse F-29, one for trailer tow left turn/brake light via fuse F-53, and one for trailer tow right turn/brake light via fuse F-81. Each or these relays receives power from the battery bus (A0) in the PDC. These relays connect to individual wires that route through the body harness connectors to the 7 pin trailer connector at the license plate area of the truck. Each relays output is routed through an individual 20 amp fuse and out from the PDC through connectors in the main wiring harness and follows the left frame rail through the main body harness connector which is located just behind the left front tire to the rear of the truck. Control power for these 4 relays is provided from the battery bus (A0) in the PDC and the relay coils are individually grounded by the BCM such that the trailer wiring and its associated power is completely separate from the trucks brake, taillight, and backup light circuits. The Integrated Trailer Brake Controller receives power from two sources. Control power comes from fuse F-87 which, unlike the other fuses, is energized from the run/start relay. Power for the electric brake circuit comes from fuse F-11 (30 amp) which is powered directly from the battery bus (A0) in the PDC. There is also a dedicated fused 30 amp (F-30) charge line that feeds the 7 pin trailer connector, but it is not relay protected. Note that this circuit is also exempt from load shedding since it is connected directly to the battery bus making it always energized. The 7 pin trailer connector is also grounded via circuit G-314 to the truck body. In conclusion it seems that the BCM is well protected as the BCM only switches relay control power for the trailer lighting circuits. Any direct short would blow the 20 amp fuse in the PDC. The only issue I can see is if trailer lighting current is high enough (but less than 20 amps) for long enough you could damage the PC Board in the PDC, however I cannot confirm that this power actually flows through the PC board as it not accessible as best as I can tell. I for one, may install smaller fuses than the 20 amp ones as my trailer uses all LED lights so the total amp draw of my lights is quite small. Cheers. Ken Irwin

 

[RikDavis]

Excellent post, and thanks for calling out the fuse numbers. I will probably just pull the charge line fuse. My own trailer has enough solar that I rarely ever used the charge line on my previous truck. I developed the habit of turning the line off when I was delivering new trailers which usually had no battery and all the lights on inside.
Am I correct that if you have a serious fault that it will be basically replace the fuse and find the fault without worrying about having a computer reset at the dealer?
I have always considered myself a fairly good electrical person but the new truck is so computerized it scares the hell out of me

 

[Kirwin]

I agree with all the computer stuff on this truck I wanted to understand how it worked. The wiring diagram shows that the charge line comes directly off the battery buss in the PDC through fuse F-30, therefore the BCM won't know that the fuse is in or out as far as I can tell. The BCM only grounds the coil side of the individual trailer lighting relays. For the circuit that had the short, the relay would close at the direction of the BCM and the fuse would just blow again if the short still existed. Keep in mind that these relays are most likely part of a PC board in the PDC, so I would probably try to eliminate the cause before I blew too many fuses looking for the short. A good DVM would be a better approach. Ken Irwin

 

[sag2]

View attachment Trailer tow, 2014.pdf

Trailer tow wiring.

 

[RikDavis]

View attachment 87644

Trailer tow wiring.

Is this info in the service manual DVD or do you have another source? I had heard the DVD lacked electrical info. Anyone who bought the DVD, what was the delivery time? Going to be heading south in a couple weeks and don't want it sitting in my mail for a couple months

 

[Kirwin]

The wiring schematics are not present in the service manual. I bought the DVD, it took about a week to get it. It does however, have the discussion that was in the front of the old wiring schematics as to how the circuit works so it is of some value to help you understand the circuits. Ken Irwin

 

[sag2]

In order to get the wiring diagrams you have to purchase subscription to Tech Authority. However if you look in the DTC based diagnostic section of the service manual, almost every fault code diagnostic has a wiring diagram for that circuit.

 

[JLandry]

In order to get the wiring diagrams you have to purchase subscription to Tech Authority.

sag2,

Are the wiring diagrams on Tech Authority configured in such a way that they can be printed (or saved) locally as a pdfs? Or are they some weird interactive media kind of thing?

I've ordered a 2014 3500 service manual on CD, but I really want to get my hands on a complete set of wiring diagrams.

Thanks,

John L.

 

[Kirwin]

sag2,

Are the wiring diagrams on Tech Authority configured in such a way that they can be printed (or saved) locally as a pdfs? Or are they some weird interactive media kind of thing?

I've ordered a 2014 3500 service manual on CD, but I really want to get my hands on a complete set of wiring diagrams.

Thanks,

John L.

You can save individual files as PDFs but there are thousands of them. I downloaded the ones I was specifically interested in but I'm of the opinion that there are too many to have a complete set. You can enter your VIN number and it will show you VIN specific information, but its still only as good as the person entering the data. Some diagrams are the same with or without entering in a VIN. I. E. They are generic for a 2013 Ram 3500 CC Dually with the diesel engine for instance. I will continue to come to the TDR and get someone with access to post them here for me thus hopefully we can all learn together. The one on this thread is an example of what they look like, they are not the old diagrams with splices called out that were in the old service manuals. They do however, show pin locations and connector call outs for each connector in the circuit so that is an improvement I think. Ken Irwin

 

[SnoKing]

What I see missing in the B+ charge circuit to the trailer is a charge relay. So if the trailer is plugged in with the truck turned off, you are still send 12V DC to the trailer battery. Even my 93 and 2001 Dodge RAMs were set up this way. Using a lot of power in the trailer, say at a Walmart over night and you are pulling charge from the trucks batteries in parallel with the trailer battery. On my 93 and 01 I installed a constant duty rated solenoid in the B+ lead to the trailer and activated it from a run circuit in the truck.

Chris

 

[Kirwin]

What I see missing in the B+ charge circuit to the trailer is a charge relay. So if the trailer is plugged in with the truck turned off, you are still send 12V DC to the trailer battery. Even my 93 and 2001 Dodge RAMs were set up this way. Using a lot of power in the trailer, say at a Walmart over night and you are pulling charge from the trucks batteries in parallel with the trailer battery. On my 93 and 01 I installed a constant duty rated solenoid in the B+ lead to the trailer and activated it from a run circuit in the truck.

Chris

Chris, I'm not sure I understand what you are saying. The charge circuit is there via fuse F-30. Are you saying that there should be a relay that disconnects the trailer charge circuit when the truck is off?
Ken Irwin

 

[SnoKing]

That is what some people prefer! Or you unplug and then remember to plug it in again. Chris

http://www.powerstream.com/battery-isolator.htm

 

[Kirwin]

That is what some people prefer! Or you unplug and then remember to plug it in again. Chris

http://www.powerstream.com/battery-isolator.htm

OK. Now I understand. Sorry I guess I'm a little slow. I unplug when I stop for an overnight. I know that's not always the best. I have pulled out without plugging the trailer back in and had to stop and plug it in when I remembered. I guess I will have to think about your isolator idea some more. Ken Iriwn

 

[JLandry]

I unplug when I stop for an overnight.

Ken,

I do this also.

I know that's not always the best. I have pulled out without plugging the trailer back in and had to stop and plug it in when I remembered.

Make yourself a checklist (like pilots use) for your RV and laminate in plastic. Go through each item on the list every single time before you leave.

The last thing on my "exterior" checklist is to test the trailer brakes by manually activating the trailer brake controller as I'm pulling out of a campsite. If I've managed to miss plugging in our travel trailer, I'll catch it then.

We actually use two separate checklists for preparing to move our travel trailer... one for my wife to use inside and one for me to use outside.

John L.

 

[Larry Willard]

I also check the brake operation each morning as I pull out, but I also walk around checking all the lights, tires, plug in etc. I also run with the lights on and that way as you look in the mirror and see the clearance lights on the side of the trailer I know the plug is still plugged in.
Larry

 

[RikDavis]

IF i unplug the cord or put down the tongue jack etc. on an overnight stop I wrap the seat belt around the steering wheel as a reminder I need to do something before I move