HELP REQUESTED: Running lights / tail lights not working

Alan_B · Nov 28, 2016

We are on our first trip with our 2016 Bighorn 3570RS. After hooking the 7-pin connector to the truck, the brake lights and turn signal lights work fine. However the running lights / marker lights and tail lights do not work. They should come on when I turn on the headlights on the truck, but they do not.

As this is our first trip, I don't know if they ever worked. This was not something I checked during PDI

(I checked the brake lights of course but not the running lights as it was full daylight at the time).

As all of these lights don't work, it must be something on the whole circuit. I am going to check the following:

Is this fuse blown on the truck? (Not likely but somewhat easy to check)
Is a fuse blown / circuit breaker tripped in the fifth wheel? Not easy to check as I don't know where the fuse panel is. Behind the basement wall, near the steps perhaps?
Maybe the 7-pin cable that runs from the fifth wheel to the truck is bad?

Any and all help would be appreciated.

Alan B.

Thanks!

danemayer · Nov 28, 2016

Alan_B said:
As all of these lights don't work, it must be something on the whole circuit. I am going to check the following:

Is this fuse blown on the truck? (Not likely but somewhat easy to check)

Is a fuse blown / circuit breaker tripped in the fifth wheel? Not easy to check as I don't know where the fuse panel is. Behind the basement wall, near the steps perhaps?

Maybe the 7-pin cable that runs from the fifth wheel to the truck is bad?

Hi Alan,

I don't think the trailer has a fuse or circuit breaker on the wiring to the running lights/tail lights. You've probably got a junction box right behind the pinbox, which is where the umbilical cord is connected to the trailer wiring. You might want to check voltage inside that box to see which side of the box needs further investigation.

Alan_B · Nov 28, 2016

danemayer said:
Hi Alan,

I don't think the trailer has a fuse or circuit breaker on the wiring to the running lights/tail lights. You've probably got a junction box right behind the pinbox, which is where the umbilical cord is connected to the trailer wiring. You might want to check voltage inside that box to see which side of the box needs further investigation.

Thanks for the quick reply. You are correct, I just checked all the fuses and none are labelled for the running/tail lights.

You are also correct about a junction box in the king pin box for the umbilical cord. I will check that in the morning.

Thanks!!

travelin2 · Nov 28, 2016

A quick and easy check to see if the 7 pin plug will illuminate your running lights is use a short jumper wire from the rigs 12v pin to the running lights pin.

If that task powers up your running lights then there is an issue with the truck
I blew the fuse for the running lights with my utility trailer. Here's the fuse found in the fuse block under the hood of my 2012 SD

Start there

Sent from my iPhone using Tapatalk

Alan_B · Nov 28, 2016

Great idea Lyle, thanks.

mlpeloquin · Nov 28, 2016

Get the trucks owner manual out and look up fuses. They should have a picture of the box and location by number. On another page there should be a description of each fuse for what system it protects. You should find the fuse in the trucks fuse box. Make sure you have several spare fuses. It may have blown because you connected it live, or their is a fault in the wiring.

Here is a URL to etrailer with the wiring connections for all different trailer connectors. https://www.etrailer.com/faq-wiring.aspx

Alan_B · Nov 29, 2016

No solution yet. I checked the fuses in the truck. Two that are labelled for the trailer running lights look OK. However the fuse and relay marked "Trailer Tow Battery Charge" are missing. Not included with the new truck. I have to put those in anyway, I will check after that.

Oregon_Camper · Nov 29, 2016

Alan_B said:
No solution yet. I checked the fuses in the truck. Two that are labelled for the trailer running lights look OK. However the fuse and relay marked "Trailer Tow Battery Charge" are missing. Not included with the new truck. I have to put those in anyway, I will check after that.

Look in your glove box and all doc's that came with truck. Odds are the fuse is in there.

TALong · Nov 29, 2016

I had the same problem last month. It was a problem in my fuse box for my tow vehicle. The fuse was missing and when I went to purchase one and install it, it wouldn't stay in. I had to bend the fuse contacts to make it work temporarily. When I took it to the GMC dealership - they determined they have to replace the fuse box. There are only two on hand in the country - it may be a long wait.

Sent from my iPhone using Tapatalk

Alan_B · Nov 29, 2016

PROBLEM RESOLVED: Running lights / tail lights not working

The trailer umbilical cord runs up to a junction box mounted on the back of the kingpin box. The wire connections in the junction box were loose. Fixing the connections fixed the problem.

So the truck was not the problem. But checking out the truck fuses exposed the lack of trailer tow battery charging relays. Now, time to find the right fuse and right relay to fix that issue! (and yes I checked the glove box and all other storage for the relay, but no go.)

Thanks to everyone for the help.

travelin2 · Nov 29, 2016

Re: PROBLEM RESOLVED: Running lights / tail lights not working

Alan_B said:
The trailer umbilical cord runs up to a junction box mounted on the back of the kingpin box. The wire connections in the junction box were loose. Fixing the connections fixed the problem.

Thanks to everyone for the help.

When I had to replace the breakaway switch on the 3010 I replaced the wire nuts with the appropriate automotive connectors...

Sent from my iPhone using Tapatalk

Jesstruckn/Jesstalkn · Nov 30, 2016

Another good reason to can the metal box and replace it with the plastic 7-way box and coiled cord.
1 - cleaner looking
2 - no more loose wire nuts
3 - no more sharp metal edges for wires to short out on
4 - easier to do testing and troubleshoot a problem
5 - no more 8' long cord hanging down a getting hung up on things.
6 - no more wrapping it up and shoving it into the pinbox to store it

Sent from my XT1585 using Tapatalk

Alan_B · Nov 30, 2016

jesstalkn said:
Another good reason to can the metal box and replace it with the plastic 7-way box and coiled cord.
1 - cleaner looking
2 - no more loose wire nuts
3 - no more sharp metal edges for wires to short out on
4 - easier to do testing and troubleshoot a problem
5 - no more 8' long cord hanging down a getting hung up on things.
6 - no more wrapping it up and shoving it into the pinbox to store it

Very nice! Did you buy this as a package, or build it yourself?

- - - Updated - - -

Jesstruckn/Jesstalkn · Nov 30, 2016

I made it myself. I have made quite a few now for fellow Heartland'ers.
It's fairly easy to make.
Not cheap though.
I could walk you through getting all of the parts to make your own or I can make you one

Sent from my XT1585 using Tapatalk

wdk450 · Nov 30, 2016

Alan_B said:
Very nice! Did you buy this as a package, or build it yourself?

- - - Updated - - -

Another option: https://www.amazon.com/dp/B01FWIFS24?psc=1

JohnDar · Nov 30, 2016

jesstalkn said:
I made it myself. I have made quite a few now for fellow Heartland'ers.
It's fairly easy to make.
Not cheap though.
I could walk you through getting all of the parts to make your own or I can make you one

Sent from my XT1585 using Tapatalk

I like that! Do you have a printed instruction sheet and parts source list? Or what is your price to build and ship? Sometimes convenience is worth the cost.

Sent from my iPad using Tapatalk

Alan_B · Nov 30, 2016

jesstalkn said:
I made it myself. I have made quite a few now for fellow Heartland'ers.
It's fairly easy to make.
Not cheap though....or I can make you one

That is a generous offer. What is the cost?

thanks!

Jesstruckn/Jesstalkn · Nov 30, 2016

PM me please

Sent from my XT1585 using Tapatalk

Alan_B · Dec 2, 2016

Trailer tow battery charge relay

Alan_B said:
No solution yet. I checked the fuses in the truck. Two that are labelled for the trailer running lights look OK. However the fuse and relay marked "Trailer Tow Battery Charge" are missing. Not included with the new truck. I have to put those in anyway, I will check after that.

A follow-up on the trailer tow battery charge relay issue. Newer (2015+) Ford Super Duty trucks no longer use the trailer tow battery charge relay in the power distribution box. There is a new separate "smart" module in the truck that controls power flow to the trailer battery. The module needs to "see" the trailer battery on the circuit to begin charging.

While this makes sense, it is now harder to confirm that there is power flowing through the umbilical cord to the trailer battery.

Unfortunately the fuse box diagram for the power distribution box still shows the locations for the trailer tow battery charge relay. There are no pins in the box to install such a relay. The manual needs updating.

HELP REQUESTED: Running lights / tail lights not working

Alan_B

Well-known member

danemayer

Well-known member

Alan_B

Well-known member

travelin2

Pennsylvania Chapter Leaders-retired

Alan_B

Well-known member

mlpeloquin

Well-known member

Alan_B

Well-known member

Oregon_Camper

Well-known member

TALong

Member

Alan_B

Well-known member

travelin2

Pennsylvania Chapter Leaders-retired

Jesstruckn/Jesstalkn

Well-known member

Alan_B

Well-known member

Jesstruckn/Jesstalkn

Well-known member

wdk450

Well-known member

JohnDar

Prolifically Gabby Member

Alan_B

Well-known member

Jesstruckn/Jesstalkn

Well-known member

Alan_B

Well-known member

Similar threads