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EagleScout-USA's avatar
EagleScout-USA
Explorer
Sep 04, 2017

Intermittent Trailer Brakes and Marker Lights

2015 Jayco Jayflight 26BHS
2009 F150 STX

Intermittent Marker Lights and Brakes on trailer

This problem happened last with only the brakes while under warranty. Tech followed wires, tested truck, took apart wheel assemblies, tested voltages, and after 2 hours of uncharged labor came to the determination "I don't know...may have not been really tight at the battery terminal connections".

Arrived home last night from a road trip. Marker lights on and off throughout trip home. Brakes on and off in conjunction with marker lights. No identified trailer hook up on prodigy controller. Didn't realize this till later in trip when going down hill. Brake lights working, turn signals and 4 way flashers all work. Last 90 minutes had no markers or brakes. Fortunately had caravan with me for supports and no time crunch to be home.

Hooked trailer up today, everything seems to be working fine, including brakes.

Followed wires as best I could. All visible wires are in good condition and connected appropriately. Rattled some of the wires on the truck and trailer, but unable to initiate outage.

Any thoughts? Moreover, would I be wasting my money taking it in for repair if I cannot present with the problem? Especially when they could not find anything last time?

I am not a diagnostician and lack confidence with electrical systems, but also value a dollar and good advise!

Thanks!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 04, 2017
    Something COMMON to both problems is chassis negative THE GROUND.

    Truck wire to socket. Check wire where it hooks to frame as well

    Truck socket.

    Umbilical cord to trailer. Does it have a pinch mark in it?

    Where umbilical connects to trailer chassis wires.

    I don't believe in miracles and the chances of 2 errors happening simultaneously in two circuits is like 10,000 times less likely than a bad ground connection.

    Print the list of "The Usual Suspects" above or even the entire response and take the rig to a DIFFERENT repair service.
  • dougrainer's avatar
    dougrainer
    Nomad
    Sep 04, 2017
    1. WHY he would pull the wheel assblys apart shows complete lack of knowledge. The fact you had BOTH running lights and brakes issues points to one thing---The 7 way connection at your Truck.
    2. I would not think the 4x4 junction box on the Jayco trailer(where all the tow plug wires go to) would be an issue as I would hope the Tech checked that
    3. The usual cause of your type problem is a rusted trailer 7 way end or your truck 7 way has a problem.
    4. An easy check is to connect your trailer to a friends truck and test drive. If the problem goes away your truck is the problem. If it stays then check the Trailer 7 way and the wiring to that 4x4 junction box which will be where the A frame is welded to the front trailer on the outside. Doug
  • mike-s's avatar
    mike-s
    Explorer
    Sep 04, 2017
    I agree that ground is the first thing to check. If the ground wiring isn't good between the TT and TV, you'll have intermittent issues, because the grounding will occur through the hitch.

    Get close enough that you can connect the 7 pin, but don't hitch up so there's no direct contact between the TT and TV, just the 7 pin. If the cabling is good, all the lights and brakes (have someone near a wheel listen for clicks as you work the manual control) should work.
  • John_Wayne's avatar
    John_Wayne
    Explorer II
    Sep 04, 2017
    Take a set of jumper cables hook one end to the truck making a good contact( bare metal ) do the same to the trailer side if problem goes away it's a ground problem.Fix the problem in the plug ends OR run a separate ground wire till you have time to fix it.
  • EagleScout-USA's avatar
    EagleScout-USA
    Explorer
    Sep 09, 2017
    Thank you for all of your replies. I took my truck to the local U-Haul and shared with them the insight that was provided here. They confirmed a bad 7 plug outlet. Also the harness to the plug was frayed and some of the wires were bad. Under $50 and out the door!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 09, 2017
    Sometimes I wonder if there are any other forums on the web that have the technical expertise displayed on this one? This question is derived from pure curiosity and nothing else.
  • wnjj's avatar
    wnjj
    Explorer II
    Sep 09, 2017
    I didn't see this thread until the OP already got it fixed but to those suggesting "ground", how can you explain functioning brake lights?

    Granted, bad grounds are often the cause of issues, especially mysterious ones but this was clearly not one of those from the original description.

    Thanks for reporting back, OP!
  • dougrainer's avatar
    dougrainer
    Nomad
    Sep 09, 2017
    wnjj wrote:
    I didn't see this thread until the OP already got it fixed but to those suggesting "ground", how can you explain functioning brake lights?

    Granted, bad grounds are often the cause of issues, especially mysterious ones but this was clearly not one of those from the original description.

    Thanks for reporting back, OP!


    Because "Checking the Ground" is ALWAYS what people with lack of knowledge state to do. As a professional RV Tech. GROUND's causing problems are extremely rare. Besides, on a trailer, even with the grease on a 5th plate or Tow BALL, that is enough to complete a ground to operate the Trailer lights. Doug
  • EagleScout-USA's avatar
    EagleScout-USA
    Explorer
    Sep 10, 2017
    Just wanted to put a good word out for the U-Haul company that did my service. I wasn't sure if they involved in these areas, but they told me they do take care of all towing needs on the tow vehicle end, at least here in suburban Buffalo. They have technicians that do these things all day long and I was told the equipment and expertise to diagnose and repair these issues. Moving forward, I would recommend checking with your local U-Haul before checking back in at the RV dealer when the suspected culprit is your tow vehicle. That labor rate was significantly cheaper, and the only thing the technician does at the facility is work in hitching and wiring all day. Of course, this goes without saying....the recommendation is for people like me that need help in these areas. Thanks again!

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