Running lights issue

[FF/PM]

I hooked up my 5er, took it to the shop and noticed all the running lights were out, but the brake/flashers worked and the battery charged. Found a blown fuse in the tow veh, replaced it and drove home. 8 miles later the fuse had blown again, same light/power issues.

Where do I go to look for the problem on this? Pretty sure based on what I've seen it is a trailer problem, but open to all suggestions.

[Tbos]

I’m guessing you have a short at one of your lights. You’ll probably have to remove each one to find the issue. There’s probably a smarter and easier way to check them but I can’t think of it right now.

[Ken / Claudia]

Sounds like a short due to a bad ground, but where that will take you or a tech some time to find. As said I would start with each light and look for a bad ground there 1st.

[JRTJH]

It "could be" anything from a loose wire at the 7 pin terminal block that's touching ground and blowing the fuse to a screw through a wire "somewhere" that "the wire runs" thoughout the trailer. Trying to pinpoint a "best chance of finding it easily" solution is impossible because there's no reliable way to determine what, where, how the short is occurring.

It'll take time and troubleshooting to find it. How much time? Depends on how lucky the tech happens to be. There are 13 clearance lights, two tail lights and a license plate light, all connected to the tail/running light circuit. It could be any part of that supply circuit, a wire in the belly or even in the ceiling.

That said, if it's a loose/shorted ground, it wouldn't blow the fuse, so it's not in the "grounding system". It's a 12 VDC short to ground (in the +12VDC side of the lights), it is probably located in the supply line "somewhere" from the terminal block on the pinbox/trailer tongue or in a wire "further back" from that location.

Good Luck tracking it down, it could be anywhere (literally)

[HitFactor]

Inspect all of the external wires, look for chaffed, cracked or missing insulation, loose connections, etc.

Are any 12v fuses blown in the trailers power center? Answer to this should help to localize the short to ground.

You can jumper the plug (on trailer) for the TV with a fuse, there is a YouTube video on how. This would take the truck out of the equation.

Pull all the lights, replace fuse(s) as necessary with a good fuse. I would probably leave all the high lights alone for the first go round. Then break out the ladder if necessary.

Turn on lights, hopefully fuse doesn't blow right away. Replace each bulb.

[bobbecky]

The internal 12 volt system is totally isolated from the outside running/turn signal/brake light system, so the inside power center will do nothing for troubleshooting a short in the running lights. The tow vehicle provides all the power to make all the outside lights I described work.

[HitFactor]

The internal 12 volt system is totally isolated from the outside running/turn signal/brake light system, so the inside power center will do nothing for troubleshooting a short in the running lights. The tow vehicle provides all the power to make all the outside lights I described work.


It will if you jumper as I suggested. https://letscampsmore.com/running-lights-hack/

That takes the truck out of the equation. Now you hunt the shorts on the trailer. If none, start hunting for shorts on the truck.

Any blown fuses in the trailer power center could be a clue as to a location with damaged wires.

You need to keep an open mind when chasing down shorts. Peeling back the skin is the last thing anyone wants to do.

[Frank G]

I had a 06 F-150 with the same Issue, Good Luck, sold it. Trailer lights worked on every other vehicle, plug it into the 06 "BAM" blown fuse. After replacing the fuse one day the ECM died and something in that fuse block went out. Dealer replaced both, Ouch, never hooked another trailer to that truck again.

[FF/PM]

I inspected all connections, cleaned and greased. I jumpered it, no issues. I replaced the fuse under the dash, ran it, with and without blinkers, ran the slides, all the lights in and out. 20 minutes later, no issues! The only thing I didn't do was move it, but the first time it didn't need to move either.

Probably no way to know until it actually stops working?

[HitFactor]

Probably no way to know until it actually stops working?

Hopefully that's a long time from now.

[Ken / Claudia]

John,
Thanks for the infor about a 12v system does not blow a fuse if shorted. I thought it has for me in past grounding issues. I could be wrong. I did blow fuses when I tried to ground a 12v hot lead to the negative battery post a couple weeks ago. I was installing LED backups lights on my newest truck. Long story, but I figured it out quickly after the 2nd fuse blew. Do not hire me to wire your truck. Nothing was ruined but 2 fuses.

[MarkEHansen]

If you short the +12 line to ground, you're definitely going to blow a fuse or let the magic smoke out of something.

[JRTJH]

...
... if it's a loose/shorted ground, it wouldn't blow the fuse, so it's not in the "grounding system". It's a 12 VDC short to ground (in the +12VDC side of the lights), it is probably located in the supply line "somewhere" from the terminal block on the pinbox/trailer tongue or in a wire "further back" from that location.

John,
Thanks for the infor about a 12v system does not blow a fuse if shorted.

If you short the +12 line to ground, you're definitely going to blow a fuse or let the magic smoke out of something.

It looks like some "clarification" is in order.

First, Ken, I NEVER said a shorted +12VDC circuit won't blow a fuse. So, Ken, you mis-read what I said.

Second, Mark, you're right, any +12VDC circuit that's connected to ground will provide a direct path to ground and if there's no load in the circuit, it will blow a fuse or, as you stated, "let the magic smoke out".....

What I said, is: If you run a screw through the ground wire or crimp it and "short the ground to ground" it won't blow a fuse..... That means, at least to me, that if the OP's clearance light circuit is blowing fuses, it's not in the ground side of his light wiring, it's in the +12 VDC side. Take a look at the post, it's pretty much self explanatory, but hopefully this will "further the clarity if there's any fog left"......

[Ken / Claudia]

I was confused, but not now. Thanks Ken

[geeman]

It will if you jumper as I suggested. https://letscampsmore.com/running-lights-hack/

That takes the truck out of the equation. Now you hunt the shorts on the trailer. If none, start hunting for shorts on the truck.

Any blown fuses in the trailer power center could be a clue as to a location with damaged wires.

You need to keep an open mind when chasing down shorts. Peeling back the skin is the last thing anyone wants to do.

IF you do try to find the problem using the "hack", make sure you use a fuse to cross the 2 leads. Otherwise that is 12v from your camper batteries. With a short, you may find it by looking for the smoke :cool: :popcorn:

I just take a spade type fuse and twist the 2 terminals. I actually have a self resetting fuse I use.

[Rubicon100]

I had a similar problem and after checking all of the bulbs one by one I came across one that had a lot of water in it.
I cleaned up the socket and used some dielectric grease then made sure to seal the light cover.

[jimborokz]

It will if you jumper as I suggested. https://letscampsmore.com/running-lights-hack/

That takes the truck out of the equation. Now you hunt the shorts on the trailer. If none, start hunting for shorts on the truck.

Any blown fuses in the trailer power center could be a clue as to a location with damaged wires.

You need to keep an open mind when chasing down shorts. Peeling back the skin is the last thing anyone wants to do.
Nice hack, I will use it on the day before I hook up and leave to check all running lights in case I have to dig out a ladder to change a high one.

Also, I once had issues with an SOB and started checking lights. Found a tail light where the lens was leaking and water had infiltrated and filled it up to the socket which by then was rusted and coroded causing a short. In my case I had to replace the light but if you catch is soon enough a cleaning may do the job. I then drilled drain holes in the bottom of the lens.