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Trailer brakes stop working when headlights are on

cbwallace
Explorer
Explorer
My Reflection has developed an issue where the trailer brakes stop working when my headlights are on. In the truck I get a Check Trailer Wiring message. When this occurs the trailer brakes don't work. When I turn the headlights off trailer brakes work again. On may last trip this also happened about 50% of the time I used a turn signal. I have checked 7-pin connector and find no corrosion. I am thinking it is a grounding issue but not sure what to check in the 5th wheel, any suggestions?

Chris
Chris, Barb, two girls, a Yellow Lab and a Sammoyed
2013 Chevy Silverado 2500 HD Duramax Crew Cab 4X4
B&W Turnover Ball w/Anderson Ultimate Hitch
2019 Grand Design Reflection 31MB
2007 Crownline 252 EX
Kayaks, Quads, Bikes and anything else we can drag along!
12 REPLIES 12

RCMAN46
Explorer
Explorer
Try connecting to a different trailer and see if you have the same problem.

jodeb720
Explorer
Explorer
i had a similar problem on my Chevy 2003 2500hd.

There's a flasher control module that went bad and exhibited a similar issue.

When I stepped on my brake lights, the right turn signal didn't work. When the clearance/running lights were on the right turn signal wouldn't flash.

I just replaced the control module and the problem abated.

Just something to think about...

cbwallace
Explorer
Explorer
Sorry, for not providing any updates as I was in the process of moving my daughter into college and getting her settled in. I tried several different testing methods including looking for a bad ground, connecting a separate ground from trailer to truck, hooking up another truck to see if it had a similar issue and even having a mobile RV tech come look at the issue. No luck! Appears it may be an issue with the IBC itself.
Chris, Barb, two girls, a Yellow Lab and a Sammoyed
2013 Chevy Silverado 2500 HD Duramax Crew Cab 4X4
B&W Turnover Ball w/Anderson Ultimate Hitch
2019 Grand Design Reflection 31MB
2007 Crownline 252 EX
Kayaks, Quads, Bikes and anything else we can drag along!

wa8yxm
Explorer III
Explorer III
agesilaus wrote:
A short somewhere in the wiring? I just spent an afternoon patching my cable after it got some road rash


Love answers like this (knee jerk) because.

NO it is not a short.. it's an open.. ground

YOu have a poor/bad ground return between trailer and truck. I've had to improve a few of the ground over the years.

The ground can handle current from Brakes OR lights but not both.

TO TEST (yes there is an easy test) you need nothing more than a SINGLE (black lead if you have the choice) automotive jumper cable Though any decent jumper cable will work

Hook one end to any non-painted part of truck Example a heavy bumper if not painted. (you can use test lights to verify good ground )
The other end to any non-painted part of trailer (Frame or tongue)

Then see if it works right. if so. improve ground.
Home was where I park it. but alas the.
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dougrainer
Nomad
Nomad
Your 7 pin SHOULD have a ground wire that connects both the Truck and the Trailer. IF NOT, then the 5th hitch plate is the ground between the 2, which is NOT adequate. Do NOT connect the trailer to the truck. just have the hitch off the plate and then connect the 7 way and see if you get tow lights and brake lights and brake operation. You can move slightly a foot or so to see if the brakes grab. That will determine the ground situation without testing the 7 way plug. Usually the ground from the Trailer end is secured to a screw in lug in the 5th wheel hitch tongue. Doug

Harvard
Explorer
Explorer
Sounds to me like the Brake Controller is wired incorrectly.
Maybe the Ground Wire of the Brake Control Module is connected
to the wire that goes to the Park Lights.

With the Park Lights off the Brake Controller gets its
0 VDC through the park light bulbs to Ground.

When the Park Lights are turned on there is no
0 VDC for the Brake Controller.

MEXICOWANDERER
Explorer
Explorer
Short to blue tow vehicle lights would go wacky
Short blue to the negative breaker or fuse operates

enblethen
Nomad
Nomad
I miss read the original post. Read as if it was brake lights and not the electric brakes.
Does sound like the system is backfeeding. It could be ground or a short between the brake (blue) wire and the tailight wiring.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

MEXICOWANDERER
Explorer
Explorer
A restricting negative is easy peasy to diagnose

Turn on parking lights, then actuate the manual brake lever on the controller. What happens to the lights on the trailer?

If the circuitry goes "Bates Motel" with the lights on the trailer you gotcha problems with the chassis negative.

Start the exam process by opening the plug and look for the usual suspects.

enblethen
Nomad
Nomad
Try pulling the brake lamps in the trailer. It could be a bad filament shorting to the tailight filament.
Test trailer with jumper wire from trailer battery to light functions. Look for anything odd in lighting.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

beemerphile1
Explorer
Explorer
I agree about it probably being a ground issue. Did you test the resistance from the ground wire in the umbilical and the frame?

Look underneath and check/clean/reattach all the ground connections on the frame.

How about the truck side? Is it grounded to the frame somewhere in the rear?
Build a life you don't need a vacation from.

2016 Silverado 3500HD DRW D/A 4x4
2018 Keystone Cougar 26RBS
2006 Weekend Warrior FK1900

agesilaus
Explorer III
Explorer III
A short somewhere in the wiring? I just spent an afternoon patching my cable after it got some road rash
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