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02 Silverado Trailer Brakes/Lights Phenomenon



Hi Folks,


I sure hope there’s someone out there who can help me with an electrical issue that I’m having with my truck. I surfed the internet for 6 hours and couldn’t find anyone who experienced the same problem. Any input would be greatly appreciated.


I’ve got a 2002 Silverado with the factory trailering package and 7 way trailer harness. I’ve towed several trailers over the years with no electrical difficulties. I recently purchased a newer horse trailer equipped with electric brakes. Up until now, all of my trailers either had no brakes or had hydraulic surge brakes. I picked the new trailer up a few weeks ago and all of the trailer lights functioned appropriately. Since most of my trips since then were short, I hadn’t yet installed an electric brake controller, up until last weekend. My truck came equipped with the pigtail that connects to the fuse block under the dash and requires splicing to the brake controller. I purchased a Dexter Axle DX2 Predator brake controller and followed all of the instructions. I connected the wires according to the manufacturer’s color-coding diagram and ran the unit through the preliminary testing without a trailer attached. All tests checked out perfectly. I connected my truck to the trailer, attached the trailer plug and re-tested all of the lighting. Again, all went perfectly.

I began to tow the trailer down my road and first tested the controller’s emergency brake function by operating the “manual” slide. As expected, the trailer tugged, the digital read-out climbed and the vehicle came to a stop. Next, I picked up more speed and then depressed the vehicle’s brakes. I didn’t feel a response from trailer brakes as I had with the manually operated brake, recognizing that the resistance was going to be significantly more subtle. What I also noticed, was that there was no digital read-out. So I turned up the power wheel adjustment to the maximum range and stopped the vehicle again with even greater pressure, but still felt no resistance from the trailer and again, no digital read-out.

Upon reaching my destination, I discovered that now my trailer lights were no longer operating correctly. And when I depressed the brakes, all of my marker lights would slowly, but dimly illuminate. When I disconnected the trailer plug, I also discovered that my brake lights on the truck wouldn’t come on anymore when I activated the manual brake on the controller – although my cab brake light still did.

So the investigation began. I first wanted to rule out any electrical issues with my trailer. So I took my wife’s 2004 Tahoe and connected it to the same trailer. All lights on the trailer functioned perfectly normal. I called Dexter Axle and spoke with an Engineer there, who confirmed that my controller wiring was indeed correct. The fact that my digital read-out quit functioning once I connected the truck to the trailer and even after disconnecting it from the trailer led him to believe that there was no power being sent to the controller once the brake pedal was depressed. Evidently, when the brake pedal is depressed, the light blue wire (CKT #1620) should receive power from the tow vehicle’s brake lighting, sending it to the controller to both activate the digital display and trailer brakes. So I climbed back under the dash and verified that he was correct. Here’s what I have:

There are 4 wires coming off of the controller unit.

- BLACK (receives a 12 volt supply from the tow vehicle)

- RED (sends power to the stoplights)

- BLUE (sends power to activate the trailer brakes)

- WHITE (Ground)

There are 5 wires coming from the brown connector that connects to the fuse block under the dash:

- RED (fused 12 volt supply that connects to the controller’s BLACK wire)

- LIGHT BLUE (vehicle stop lamp switch to brake controller input that connects to the controller’s RED wire)

- DARK BLUE (trailer brake controller switched output connects to the controller’s BLUE wire)

- BLACK (brake controller ground that connects to the controller’s WHITE wire)

- BROWN (brake controller illumination – this wire is unused)

Here is what I found while using the voltage tester against the leads exiting the brown connector attached to the fuse block, using the vehicle as ground:

RED = showed a continuous 12 volt supply

LIGHT BLUE = showed no power when the brake pedal was depressed

DARK BLUE = showed proportional voltage increase when the manual emergency brake lever was activated on the controller

BLACK = ground confirmed


So now I not only don’t have functioning trailer brakes, but my trailer lighting system is totally screwed up. I checked every fuse in the instrument panel and under the hood and found nothing to be blown. It’s probably something simple that I’m overlooking, but I’m just completely stumped. Nothing else had been modified or tampered with aside from what I’ve mentioned above. Thanks in advance for any help.


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I discovered that the CHMSL fuse in the U/H Electrical Center was blown. Changed the fuse and fixed a grounding issue in the 7-way trailer connecter and I'm back up and running. Of all the terminals in the truck's 7-way trailer connector, the ground terminal was the only one that was corroded. The connector is a sealed unit, but apparently allowed water and salt to pass at some point. Thanks for the help.

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Ok - I have to be honest with you -- I read about one paragraph of your post, so my apologies if this is not regarding lighting.


So, with that said, the most common problem I see with trailer wiring issues that throws even the most seasoned electrical gurus off, is bulb issues. Another area of manufacturing these days which isn't what it used to be ....


What I mean by that is, you have 2 filaments in the bulb - one for running, one for stop/turn. One filament burns out on one side, detaches from the post, then welds itself to the other, effectively creating a short circuit. This will make your running lights blink, one stop light not work, or any combination of strange problems - even with a brand new trailer. Check ALL dual filament bulbs for this ... and when in doubt, replace them - they're cheap enough. Normally that can easily be spotted visually, depending on your eyesight - they're pretty small.


The second most common issue is a poor ground between either the truck & trailer, or between the trailer & the lights themselves. Make sure you have continuity to ground from the socket, all the way to the frame of the truck -- zero to .2 - .3 ohms max. Any more than that & you'll need to do some sanding or wire-wheeling of ground points until you get those numbers.

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