Trailer lights trouble

I am stumped with my trailer lights so I’m asking for advise. Here’s the situation
2003 1500 Silverado
All lights work on truck
Shore lander trailer, original wires

No Right Brake light

Everything else works
Running, turn , flashers..all lights on the trailer work. But no Right Rear Brake

I have done the following..
New oem plug on truck
Cleaned all the ground wires…both lights and trailer. Emery cloth and wire brush.
Checked all the wires on both lights.. took them apart and cleaned wires and reconnected.
Cleaned the four pole flat plug on trailer, emery cloth again..

Still no right side brake.

I’m stumped..any suggestions ?

Thanks

Have you tried one of the little flat 4 tester plugs with LEDs? For $5 that will at least tell you if the issue is with the vehicle or trailer.

dirtywater wrote:

Have you tried one of the little flat 4 tester plugs with LEDs? For $5 that will at least tell you if the issue is with the vehicle or trailer.

X2

Mike, I had something similar happen to me that you are currently experiencing. Turns out there was a slight short on the trailer light that blew my truck fuse. It happened intermittently and was irritating.

Id bet it is that or the need for a jump ground between metal trailer components.

dirtywater wrote:

Have you tried one of the little flat 4 tester plugs with LEDs? For $5 that will at least tell you if the issue is with the vehicle or trailer.

Yes, get this ^^^.

Make absolutely sure you haven’t missed a cryptically labeled fuse that is blown. I drove myself crazy trying to find why my trailer running lights weren’t working, turns out they were on a separate fuse that the manual only called out as TRRL. As if that is the globally recognized standard for Trailer Running Lights and everybody would know what that means.

BTW are these incandescent or LED trailer lights?

Assuming you verify all is good with the vehicle and power is getting to the plug, the situation gets pretty strange.

No running lights or no brake/turn would be easy, one filament burned out in the 2 filament bulb. Replace the bulb. But since the turn signal and the brake light use the same filament… hmmm.

I would still put in a new bulb at the right side and see if something has gone bad with the bulb or the socket.

Next, I would use a multimeter to check what is going with the tail light by probing the green wire. When the brake is pressed, you should see 12 to 16 volts steady and when the turn signal is on you should see the same voltage but pulsing.

Where we go next depends on what readings you get.

Grouse

Lot of issues that can cause this,from bad connections,grounds,turn signal switches,etc.
If you can’t figure it out swing by the shop and I will help you.

Ironic that it’s the right brake. Same pita I had twice. Both times it was in my “Y” adapter for my rv plug and trailer plug

Lots of Silverados have separate fuses for turn/brake lights. Not sure what year they started doing it this way. 1 fuse for left side and 1 fuse for right side. Look under the hood in fuse/power box.

Bulbs are incandescent

I have checked all fuses in the truck and everything looks good.
I have also switched bulbs from left to right and the same bulb works on the left side. The same bulb even works with the flashers on , both sides .

Everything works on the truck as far as lights go.

I will check the truck plug….but its brand new as of tonight.
I will also see if I can change the socket in the right trailer light.

You need to bust out a multi meter set to 12vdc or a 12v test light, and check power coming out of the truck plug: white (ground) and green ( RT turn/stop). You can also check the trailer wiring by hooking up a 12v battery to the trailer white and green at the plug, I bet the trailer is Ok because you have Right turn (same filament in the bulb as break light). Like stated above there is multi fuses for the trailer under the hood of the truck. You say they “look good” but the only way to test them is with test light on both sides of the fuse. The fuse could be good but corroded terminal or broken wire in the fuse box.
Keep us updated

Your 2013 silverado has separate fuses for the trailer blinkers. Yes it seems odd but same exact issue with my 2010 a few years ago. Check your fuse block map and find TRLR BLNKR or TRLR SGNL fuse (i forget how they coded it but it’s one of those)

Mike, tucked up at the rear of the frame near the bumper should be a tail light circuit board. Looks like the one in the link below.

Given its a 2003 and the years of crap salt getting into everything, IF you isolate it to the truck wire harness, you most definitely want to test this. The harness along the frame goes to this, and this works as a splitter. Everything on the truck can work perfect and no voltage to the trailer receptacle. If salt gets in this, the pins corrode and rot away. Had to replace this on a ’01 and a ’04

https://www.carparts.com/details/Chevrolet/Silverado_1500_HD/Dorman/Tail_Light_Circuit_Board/2003/RB923012.html?TID=gglpla&origin=&utm_source=google&utm_medium=pla&utm_campaign=12190938700&gclid=Cj0KCQjw5JSLBhCxARIsAHgO2SeUF3x6Cdamuw0tVarIEQ4X34-OOM4138yj26GUlKf-rc2QQXzNup4aAtPoEALw_wcB&gclsrc=aw.ds

Trailer is fine. Hooked up to different vehicle and worked. So it’s the truck.
No voltage to green wire at the plug. I have checked fuses in the dash. I didn’t see any trailer fuses under the hood. I’m digging a little deeper this afternoon. I will look for the block Randy mentioned. And check all plugs on the harness in the area.

Oh sorry it said 03, I read 13 in my head. Disregard what I said

Located the tail light circuit board by the spare tire. Replaced it and still….no brake…
So its in front of that.

Mike Burke wrote:

Located the tail light circuit board by the spare tire. Replaced it and still….no brake…
So its in front of that.

That stinks.

Are you positive all fuses are good? You said you checked them, but was that just a visual inspection, or did you actually swap in a new fuse with no results?

Looking at the manual, there are trailer lighting fuses located in all 3 separate fuse panels. Why they couldn’t put all the trailer fuses in one places is beyond me. There are two different fuses that look like they could be involved in the right trailer brake:

1) On the fuse box on the left side of the instrument panel, look at RT TRLR ST/TRN — that’s right side trailer stop and turn signal. (Seems unlikely since your signal works)

2) On the center fuse box under the instrument panel, look at TRAILER — that’s trailer brake wiring (Again, since the left brake works that seems weird)

If you’ve definitely ruled out the fuses, you’re in for some fun trying to track down the short in the wiring between the fuse panel and the plug at the back.

I am going to start replacing fuses even if they look good. I only see two fuse locations..
Left side by drivers door…that’s the one with four fuses…as you mentioned

And I don’t see any trailer fuses under the hood fuse location.
2003 Silverado 1500

Its going to my mechanic Friday…I’m at a loss here.

Thanks

Looks like Fuse #9 under the hood is trailer stop/turn

https://chevytrucks.org/1999-2006-chevy-silverado-sierra-fuse-box-diagram/

Mike Burke wrote:

I am going to start replacing fuses even if they look good. I only see two fuse locations..

Do you have a multi-meter and/or a test light? Just going by looks doesn’t always do it.

Test lights are super cheap and they make doing certain checks for power and ground very fast and easy. They are about $5-7. Super handy tool for trailer light diagnostics.

Fuses now have test points on top that allow you to use a test light (or multimeter to test them for power without pulling each one out:

My money is still on fuses, but there is another possibility. I believe there are also some relays in GM trucks that are non-serviceable and are part of the fuse-block circuit board. Not a DIY fix, but worth mentioning to your mechanic.

Grouse

I agree with Grouse. I bet it’s a fuse too. Mike, before you go throwing fuses or parts or whatever at it. Try swapping the fuses on the side that works with the side that doesn’t if you don’t have other tools available. Isolating the burnt fuse should be easy doing this.

Once isolated, figuring out why it blew is another reason all together. Having a slight short in a trailer light or wiring can burn out a fuse in time while it may work on a different towing vehicle.

maybe its just the brake lite side of the bulb burnt out

gimp wrote:

maybe its just the brake lite side of the bulb burnt out

He tried the trailer on a different truck and everything worked. The turn and brakes use the same filament in the bulb and the turns work so its not the bulb.

I have right side brake light again !!

Turn Signal Flasher Module

I had read one post online some place, that a guy had the same problem with his. So I took mine out and cleaned it but that didn’t work. Mechanic said it was bad so they replaced it. Works now.