Trailer lamp fault problem
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Trailer lamp fault problem
2023 F150 XLT - have A.R.E. cap installed -- 3rd STOP light module was connected to TRAILER electrical connector and interior LEDS direct to battery by ARE dealer-
Have had scattered problem of 'trailer right(left) lamp fault' display since 2024 - now its almost continuous (and removes color space bars on backup camera screen) -
Ford dealer says its the cap lighting module causing the now almost continuous fault display since recent software upgrade was applied by dealer a few weeks ago.
BTW no trailer has been connected to truck in past 9 months. Impossible to stop display showing on random basis - service rep saw it for himself and on video.
Dealer's tech said to disconnect the ARE CAP module and go direct to left rear light housing to 'see if that helps'... they would charge me $$$ if they had to solve the problem!
Also told that the Ford Electonics Transmitter (FET)? monitors any abnormal draw on electrical connections and display faults.
Last year I tried to upgrade to LED STOP/TURN lamps and got nowhere with fault displays - also tried installing a STOP/TURN/BACKUP light bar under tail gate, connected directly to TRAILER connector - - - the lights went crazy - had to remove light bar and send back for refund...
Any one else with FET fault experience - mother FORD will not let me add anything they don't sell -
Have had scattered problem of 'trailer right(left) lamp fault' display since 2024 - now its almost continuous (and removes color space bars on backup camera screen) -
Ford dealer says its the cap lighting module causing the now almost continuous fault display since recent software upgrade was applied by dealer a few weeks ago.
BTW no trailer has been connected to truck in past 9 months. Impossible to stop display showing on random basis - service rep saw it for himself and on video.
Dealer's tech said to disconnect the ARE CAP module and go direct to left rear light housing to 'see if that helps'... they would charge me $$$ if they had to solve the problem!
Also told that the Ford Electonics Transmitter (FET)? monitors any abnormal draw on electrical connections and display faults.
Last year I tried to upgrade to LED STOP/TURN lamps and got nowhere with fault displays - also tried installing a STOP/TURN/BACKUP light bar under tail gate, connected directly to TRAILER connector - - - the lights went crazy - had to remove light bar and send back for refund...
Any one else with FET fault experience - mother FORD will not let me add anything they don't sell -
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Joined: Dec 2013
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From: SC
There's a dedicated wire for connecting the CHMSL, center high mounted stop light. You typically can't connect to the trailer brake circuit without causing some kind of operational issue. I don't know about the 2023 but on the previous generation there is a capped purple wire underhood on the harness above the left side wheel well, and/or another tap point behind the left front kick panel.
Editing to add link to post for previous generation. Current gen may be the same, I don't know.
https://www.f150forum.com/f118/wirin...-light-480920/
Also it's very easy to connect the topper's LED light to the truck's bed light circuit if you have bed lights. Then you can just leave the topper led turned on and control it from the bed light button/switch. Also I replaced the dinky little LED my A.R.E. came with with an LED panel like is sold for RV lighting like this. Of course mine is older and was a single LED strip that could barely cast a shadow not some of the full options like they have now.
Editing to add link to post for previous generation. Current gen may be the same, I don't know.
https://www.f150forum.com/f118/wirin...-light-480920/
Also it's very easy to connect the topper's LED light to the truck's bed light circuit if you have bed lights. Then you can just leave the topper led turned on and control it from the bed light button/switch. Also I replaced the dinky little LED my A.R.E. came with with an LED panel like is sold for RV lighting like this. Of course mine is older and was a single LED strip that could barely cast a shadow not some of the full options like they have now.
Last edited by SSellers; Jun 15, 2026 at 10:59 AM.
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Junior Member
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From: Atlanta Area
I had the same trailer light fault message on my 2025 with Curt auxiliary LEDs on my bike rack. It would happen at a traffic light when the truck would restart via the Auto Stop/Start feature. I turned it off and problem solved. Ford then came out with a trailer module update and this seems to be the permanent fix. So perhaps an overwrite of the module software may help.
That said, it has happened a couple of times since but it seems to be related to user error/poor connection in the connector at the bumper. I've just pulled over, unplugged and replugged firmly, and it's fixed.
That said, it has happened a couple of times since but it seems to be related to user error/poor connection in the connector at the bumper. I've just pulled over, unplugged and replugged firmly, and it's fixed.
Last edited by MarkEm51; Jun 16, 2026 at 08:03 AM.
Senior Member First F150
Joined: Apr 2020
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From: Boston, Ma
***ellers You are right about that hidden extra wire under hood. See video here. Seen it used with headache racks and caps:
Don't let anyone mess with the trailer lighting system. I'm convinced that will lead to nothing good. E
