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Towing with 2025 6.7 Cummins

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Gunnysarg7156

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Just purchased new 2025 6.7 Cummins. Have had quite a few Cummins throughout the years to include 2003 HO 5.9, 2006, 2007.5, 2014 HO with Aisin, 2020 HO with Aisin and know the new updated HO with new 8 speed tranny. By far, the absolute best ride and power I have ever purchased. However, the truck currently has 760 miles and had to wait for the 500 mile breakin before towing. Yesterday (7/22/25) was my first hook up to my 18' aluminum fishing boat I've owned new since 2020. My previous truck before this one was 2023 Ram 2500 Rebel 6.4 and loved the truck but it was a gasser...'Nough said. Issue I'm running into is I connect the boat trailer tongue to the hitch which is also my ground for the lights. The trailer has a factory installed 7pin connector for the trailer lights and surge brakes. Plug in 7 pin connector and no trailer lights. Turn headlights on, no trailer lights, no turn signals, and no brake lights, nothing. Unplug the connector and try again. 1st thought, blow f30 fuse. Turned truck off and checked, no blown fuse. Reconnect everything again and now a "trailer connected" message comes on my dash panel to select a trailer type "conventional/gooseneck/ etc" and lights work on the trailer. Went fishing, no issues even after fishing and on way home. Just this evening, tried it again, hooked trailer up, installed 7 pin into outlet, no message on dash and NO trailer lights. WTF? Shut truck off, turned truck on, turned truck lights on and bingo, got trailer lights but no message on dash instrument panel. Do I need to got manually into the "trailer" menu through the dash to select trailer first or any suggestions whats going on. Son has 2023 Powerwagon and hooked his truck up and immediate boat trailer lights when connected. His does not have the "trailer select" option on his dash panel just as I had on the 2023 2500 Rebel.
 
Seems to be a known issue on the 2025s I think some had said the brake controller was at fault everything seems to run through it now… I am just going by memory from threads I have seen.
 
Could be Dash Brake lever, Brake Module, or RF hub.

Whatever it is, it's not right.

Appears they also maybe have a software coding or design issue with incandescent light loads.
 
Try this.

S

Post in thread 'Issue with new 2025… trailer connection wiring issue'

dblackwell said:
So, I have had my new 3500 for about 3 weeks now…. Shortly after getting the truck, I started getting a check trailer brake wiring and trailer brakes disconnected…. I haven’t pulled a trailer yet, so there isn’t an issue with a trailer, the issue is with the truck…. I used a multi meter and I have a constant hot 12v (as I should) but the parking lights pin shows a pulsating reading. Nothing else shows anything. I’ve taken the truck to the dealer and after checking the truck the believes the issue was a trailer brake control module… The part was on national back order, but they were...
Click to expand...
 
Ram Care is useless. After speaking with them and explaining this known issue with members on here, I was the first to complain about trailer connect and my absurd process to finally get the trailer recognized. According them, no software updates at all avail for 2025 6.7.
 
Is that normal to have the ground run back through the hitch ? Seems like a fundamentally poor ground with a lot of noise while driving.

I can't imagine using a hitch as a ground path and expect it to be reliable.
 
HarryN said:
Is that normal to have the ground run back through the hitch ? Seems like a fundamentally poor ground with a lot of noise while driving.

I can't imagine using a hitch as a ground path and expect it to be reliable.
Click to expand...

I haven't seen any modern trailer that use a hitch-ball ground for lights in forever. A 4-flat, or any other wiring connector includes a ground and the truck is looking for one. I don't think you're going to get a good read on anything using chassis/hitch-ball ground.

I think perhaps what he's saying is the ground wire coming from the 4-pin is grounded to his trailer hitch head, and that's pretty typical.

It's also pretty typical they need a little maintenance/TLC from time to time.
 
Slight update, recommended by another forum member. Last night, I applied di-electric grease to male and female to 7pin plug and since I had it out, I went through entire trailer wiring. Since it's a somewhat newer boat trailer, there are 4 male/female wire connectors for the marker lights and tail lights. Di-electric greased all this fittings. Once greased, hooked up the hitch, plug the 7 pin in and BINGO, all worked perfect as should and no pulsating lights. Sweet, got er fixed. Turn truck off, turned on several times, turned headlights on/off several times. Go out this morning, plug 7pin in and same BS, got to shut truck off to get trailers lights to be recognized and back to pulsating led trailer lights.

BTW...trailer coupler does not need to be attached to hitch ball for lights to work
 
Glad you figured it out! Good to know for my future towing needs as well. Thanks for sharing.
 
What's the 7 pin connector look like? I remember a post comparing the older vs new connectors that are recommended to use with our trucks.
 
Pic of receptacle on truck and 7pin on trailer. What's a lil diff from this truck to my last 2023 rebel is the "index" on the trailer plug was up on the rebel and now on the 2025, index is down. That rotates the contacts on the trailer plug male to the 9,1,3 and 5 position in the receptacle. Previous, it would have been 7,9,11 and 3 if that matters at all. As mentioned before the 7pin from the boat trailer is a 2020 boat trailer. Trailer does not have electric brakes (surge only) nor does it have 12v battery connect(hence reason for missing tabs on female plug). Current setup is the 12 pin on top, 7pin on bottom. Current 2025, did not come with tow tech group, so I have no use for the 12 pin feature. Previous 2023 Rebel had the same is the 3rd pic, Curt setup. I have no use for the the 4 pin on the Curt. Looks like an easy swap from the 12/7pin receptacle to 4blade/7pin but I'm not sure what to do with the 12 pin harness? Leaving the 12pin disconnected, will that through any codes or issues?
 

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I think thats the preferred/recommended design for the trailer side so thats not the issue.
 
The fix for my truck was the Brake control switch on the dash. They replaced the Module and it didn't help. I found another owner on FB who said this was there fix. I contacted their dealer to get details and they confirmed. I told my dealer, they got the part, replaced it, and now its good to go. Now the truck is in the shop for the RF Hub going out...
 
Dblackwell.........can you post the name of the dealer (or even pm me) that finally discovered the brake control was the issue? I have a bad feeling my issues isn't going to get resolved easily without a TSB or recall as they'll be chasing ghosts. Would like all the ammo I can when mine finally gets looked at next Monday. Thanks brother!
 
Saga continues. Took truck to Ram dealer (local, not purchasing dealer) to address the trailer connection and light issues. Arrived at dealer with boat trailer so they can see 1st hand of issues. Showed service tech issues to include videos of pulsating trailer lights, 8-10 truck restarts to finally get trailer lights to work. Dealer advised they reflashed ECM, was told to wait 24 hours to see if that fixes the issues. Ok, walk out to my "fixed" truck, proceed to reconnect the boat/trailer and exact same issues. Walk back in dealership and spoke with service rep that my truck WASN'T fixed but insisted of they could do nothing further until the 24 hour clock expired then they can escalate this issue to STAR. Not sure if this sounds like a gimmick or WTF is going on nut I signed for 2 bills(warranty) that totaled $350+ the dealer bill RAM and truck not fixed. Reason I say gimmick, is why the hell can't something get fixed right and right the 1st time? 5 /12 hours obligated at dealer today, and nothing to show for as being fixed then who knows how many hours the next duration is going to take? Is this rams way of taking care of customers?
 
You're already out of your 3/36k warranty on a 2025? You shouldn't be paying anything at the dealership if you're not.
 
Have you called Stellantis customer service and get assigned a rep? They could push the dealer to replace it. My dealer replaced it just after I told them about the AZ truck being fixed with it.
 
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