No power to trailer lights

[jnissen]

Believe they monitor the ground return current. If going through the frame and ball hitch it will show issues. I’ve got to test my dual axle enclosed trailer for the first time tomorrow. Hoping I don’t have any troubles.

 

 

Follow up - Hooked dual axle trailer up the other day. No issues at all. Trailer was recognized and test ran well. Only issue was I could not see how to setup trailer profiles. Is that only available in certain trims? I have the tow controller. Not a big deal as I only have one trailer at the moment.

[300guy]

Any updates on this issue?  Having it on my 2020 2500hd denali.  

The service dept was not able to resolve the trailer running light problem on there first attemp.   They said it does not work with old trailers and told me to buy the 3rd party adapter,  which I did and running lights still do not work.   The brake, blinkers and back up lights do work,  it is only the running lights that don’t work.

I have 4 trailers and the running lights do not work on any of them,  my trailers are :

2009 horse trailer

2010 dump trailer

2015 travel trailer

2017 boat trailer.

All my trailer lights work fine with my other vehicles,  2016 Tahoe, 2018 f-150 and 2009 Duramax.

I imagine other owners are getting frustrated that their new 70k truck designed to tow,  can not tow.    I am ready to install complete old school direct wired lighting harness but really think GM should be resolving this issue as it is pretty ridiculous that oem trailer package does not work with 90% of trailers on road.   And not GM bashing ,  I think the truck is awesome in every other aspect.  Pulls like a dream.  just need lights!

 

 

[DanTN]

Took mine in for same issue....of course they can't duplicate it...says it works with a "tester".....well it doesn't with a fricken trailer.   Hooked the same trailer up to my Dads two vehicles and it works.  Go figure.

Probably the last Chevy I'll ever own.

[reo]

 

Have the same issue with my ligt bar, and lo and behold I received an answer that may work,  All you have to do is wirs a seperate plug directly to the Brake lights and tail lights.  That bypasses the computer system for the trailer lights. Sounds like it may work.

[jnissen]

Verify the ground for the trailer is clean. If system does not detect current in the ground wire it can not work. If the ground wire is bad then ground currents will attempt to go through trailer ball. Simpler systems that don’t monitor the current will likely work even with a poor ground wire.

 

Believe they monitor currents so they can detect if trailer is trying to be disconnected via theft. So there are good reasons to use the system as intended.

[TPP]

I have a new 2020 Sierra Denali and plugged in an IPA9107A "Brake force meter w/ dynamic load simulation".  This unit basically mimics a trailer.  Everything works great.  The truck even asks to setup a trailer in the app.  But when I connect a 7-pin to 4-flat converter and connect the tester...nothing.  The tester needs either the 12V Aux or the Tail Lights to power up.  Using the 7-pin connector, it uses the 12V Aux pin for power. Using the 4-flat connector, it doesn't see the tail light power (with the lights on).  This is confirmed with a volt meter.  This is obviously not a ground problem because there is no actual trailer.

 

When a trailer is connected to either the 7-pn or 4-flat connectors, they have no tail lights.  

 

This seems to be a "look at this cool tech to prevent a stolen trailer, but your trailer lights won't work" kind of technology.

[jnissen]

Why not use the standard 4 pin connector already on the truck? Not sure how this works using an adapter from the 7 to 4. Repeat with the 4 pin connector and let us know.

 

Update: Believe you said you did test it. Just not clear if you were talking the adapter out or the default 4 out?

 

BTW I’ve had no issues using either a 7 wire trailer or a simple 4 wire trailer. Both did the correct lighting. I’d verify what type of load that tester is applying for the 4 wire.

[TPP]

My truck has no 4-flat connector.  The connector cluster in the rear bumper contains a 7-pin and 2 camera connectors.

 

No tail lights with trailer connected and no power on the tail light pin -> ground.

[TPP]

I believe that the trailer anti-theft features are new on the 19/20 models.  Is the truck not recognizing the trailer and not sending any power to the pins?

[jnissen]

Call IPA at 888-786-7899. I don’t see anywhere in their literature about using the tool to test a 4 pin connector with an adapter.

If your 4 pin trailer has been tested on other vehicles (recently) and it works then I’d look if that trailer may have LED lamps. The Denali may not detect enough current. Just a guess. Thought I read somewhere that a software update was in the works or already out to lower the brake current detection.

[TPP]

I have tested this on an older truck and the IPA tester does work in this configuration.

 

Back to the problem at hand...The pins on the 7-ping connector have not power.  Tail, RT, LT.  Is the computer keeping them turned off until it recognizes a connected trailer?  How does this recognition occur? Is there a specific resistance needed.  

 

If your listening GM: Does this mean that no "standard" or "classic" trailer light tester (or multi-meter) will work?  Can you give us a workable solution?  Or is this just something crappy that owners have to deal with?  I'm frustrated and apparently other owners are too!  I would love to see a reply from GM.

[Dinoshavbabies]

I had a brief problem with trailer lights not working correctly until I selected which trailer I had connected on the infotainment screen.

[jnissen]

Try an automotive incandescent bulb between the power and ground of the 7 pin. I suspect it’s looking at ground currents. Unless you have a fuse blown for the trailer power (possible) then you should at least see continuity through the bulb and see it light and remain lit. Make sure you use the 7 pin ground and not the bumper or other spot.

 

If this works I suspect the computer needs to see some minimal current on the ground. You can try to find that minimum with various resistance loads. Sort of a PIA to debug it that way.

[ETFab]

On 11/23/2019 at 6:48 AM, Rsktm300xcw said:

Has anyone with these problems tried the trailer light module reprogram I mentioned earlier. It helped my truck a lot. I believe that it widens the acceptable amp draw of the trailer lights substantially. My running lights were drawing too much so it would shut down so I swapped all trailer lights to led. Then my brake a d signal lights were not drawing enough so it shut down so I added the resistors. Now after reprogram and new lights everything works as it should. Also eliminated the trailer disconnected message that used to show up frequently. A combination of new lights with the proper amperage draw plus the refresh has almost completely eliminated these problems.

Is the reprogram a dealer only step that you are referring to ?

[ISK]

I have a 2021 GMC Sierra AT4. I've got a ramp with castors on one end to load a sled into the bed. There are just two small LEDs on the back end of the ramp. One hot wire and one ground that are (supposed to) power both lights on when the headlights are on. No turn or brake lights, just running lights essentially. Well when I initially plug them in they both turn on, after driving for a couple minutes I get a trailer disconnected warning on the dash. So I go out and check it, the right side is still powered on but the left is out. Same process repeats itself if I turn the truck off and back on after a while. I ignored the light and left it plugged in for 20min one night only to have the alarm start blaring because the truck thought someone was disconnecting, and thus trying to steal the trailer. Ridiculous!

 

Both lights light up fine and stay on when connected to a 2019 F-250. I've checked the 4-way adaptor which is fine. I've also bought the curt 4-way adaptor with the built in resistors, same problem. I've created a "trailer profile" which didn't make a difference. Don't tell me it's a fuse or the ground, because it's 1 hot and 1 ground wire powering both and the right side is staying on. WTF? I called my dealer since it's under warranty, they've never heard of the problem and said "all we can do is test the plug and fuses". If they're fine it's an issue with your sled ramp. You should have heard the crickets when I said well it works just fine with other vehicles...