Question about brake system on truck/trailer

JeremyN

Well-known member
I was not sure where to post this, so I thought I would start here. I was hooking up my camper to the truck today, and my son said that my trailer lights looked "weird". I told him to stand behind the trailer and help me do a light check.

I unplugged the trailer from the truck, and then plugged it back in. All the running lights work perfectly.
I reached in the truck and put the brakes on. My son said both back brake lights brightened.
I put the right blinker on, and it worked good on the truck and trailer.
I put the left blinker on, and it only works on the truck. The back tail light on the trailer does not flash.
I then looked at my dash, and noticed that my information center said "Service Trailer Brake System" on it.

I have the GM integrated brake controller in my truck. So here is my question. Does this system warning mean something is wrong with the trailer brake system on the truck, or the trailer? And how do I go about figuring that out without having to spend money at a dealer?

Sorry if this is a simple thing to look at and fix. I am not real familiar with electrical systems. I just want to make sure I have brakes when I pull to the campground this weekend.

Thanks in advance.
 

Kbvols

Well-known member
Jeremy

I had a service trailer brake system on my Chevy and the trailer brakes didn't work. Turned out it was a fuse. It was under warranty so I took it to the dealer. The weird thing was I had pulled a little over 200 miles then stopped for a break and when we started back up is when we got the message. Hopefully it is something simple.


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'Lil Guy'

Well-known member
I had that happen on my trailer and the bulb fixed it. That's an awful cheap repair but make sure those brakes are OK.
 

OEFVET

Well-known member
The bulbs for signal lights are double filament meaning the running light in that bulb could work but not the signal light. I would replace the bulb and if it still gives you the same message it is most certainly a blown fuse. Your fuse for that will be in the engine compartment on the driver's side. In a square box near the main battery. When you take the cover off turn it upside down and it will tell you what each fuse is for. Keep us posted.
 

JohnD

Moved on to the next thing...
As others have said . . . replace the bulb first . . . then check the fuse.

If either of those don't fix the issue, then you probably have an issue in either the trailer wiring or in the trailer wiring control box of the truck!

Our old old trailer (ie - three trailers back - a 1978 Coachman Cadet 24) always had trailer brake problems.

The trailer brakes worked when it didn't matter, but when we needed trailer brakes the most (down hill in the Rocky Mountains) . . . guess what . . . NO TRAILER BRAKES! :eek:

That issue was with the trailer . . . and after rewiring everything, we never did fix that issue in the 12 years we owned that trailer!

And I went through two trucks with that trailer and always had that issue.

However, on my old Dodge Ram 1500 4x4 (second in the series of trucks pulling that old Coachman), I went through three wiring control boxes (mounted under the bed of the truck) that were installed by our hitch shop before we finally upgraded to a big enough control box to handle the load!

We never did figure out what was causing the control boxes to blow out, but I'm sure that it was something in the trailer that just wasn't jiving with the truck!

And after rewiring the complete brake system on the trailer . . . we still had the same braking issues and we never did figure that one out, either.

We traded that trailer in on our 2013 Heartland Trail Runner (which we just traded in two weeks ago for our new 2015 Heartland Prowler 5th-wheel), but that old Coachman is now off the road and is being used as someone's hunters cabin up in the mountains.
 

Bob&Patty

Founders of SoCal Chapter
Stop and turn are the same filment on the bulb. The issue is in the wiring or a blown fuse. Check the under hood UBC 1st with a 12V test light...key on...and turn lever on....test both sides of the fuse. Or no test light...pull the fuse and inspect it. Changing the bulb wont fix it because the stop filiment is working. If the fuse is blown and it does it again...you have a wire going to ground.
 

OEFVET

Well-known member
Not necessarily your assuming he checked the brake lights again after checking the turn signal. It costs NOTHING to check the bulb. I would still start with it.
 

Bob&Patty

Founders of SoCal Chapter
You may correct, but I would not just go buy a bulb until I knew what was wrong. But in the OP's 1'st post he stated that both stop lamps were working so that's why I made my statement. His truck has separate fuse's for the trailer. They might be under the hood (UBC) or in the fuse center on the left side of the cluster carrier (dash). IMHO, anybody that has a truck and trailer should have cheapy test light to test fuse's and electrical connections. Quick and easy....alligator clip to ground and pointy end to fuse or connector.
 

OEFVET

Well-known member
I agree that's why I travel with a tool chest in my toy hauler. I have tools to handle just about anything.
 

fritzwell

Active Member
If the right side works, move that bulb to the left. If it works buy new bulb, if not check the socket with a meter or test light.
 
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