2018 RAM 2500 With No Running Lights

[mike.v.lanzoni]

Headlights work, actual brake lights work, license plate lights work (constant on), and turn signals work but rear running lights will not illuminate.

Cab clearance lights are also not coming on.

When I plug in my trailer, only the trailer brake works, no lights whatsoever.

I have had LEDs in all these places for several months with no issues.

I cannot locate a loose connection or burnt fuse.

If I only had to drive the truck during the day with no trailer, maybe not such a big issue, but I need to pull a trailer and have working rear running lights due to work and such.

Any known issues with the BCM or something on this?

I find it highly odd most functions still work, except for the trailer.

I could not locate anything on this partial functionality and am not sure what the heck else to look at.

Any advice or direction is much appreciated!

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[18ram67]

It sounds like you upgraded the lights to LED, not from the factory.

If so, that's your problem - about 85% certain.

These trucks have a temperamental CANBUS system.

If you got cheap lights or a non-reputable company, you're going to have these issues.

I have seen people use the ALFAOBD to activate the LED lighting option within the computer.

That might also help you.

If I interpreted that all wrong, terribly sorry, I won't be able to help you.

I'm not an electrician, LOL.

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mike.v.lanzoni I’m no electrician either but like to think I covered all the bases. Just seems odd I would suddenly lose that functionality

10-02-2021

mike.v.lanzoni True, they are actually 5th gen LED tails and harnesses I got from retro shop. They have worked great for months. I’m

10-02-2021

[AK Bob]

I would recommend swapping the LED lamps back to stock first to see if the issue is then resolved.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon auxiliary fuel tank.

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[mike.v.lanzoni]

I tried swapping back to the factory lights today, and the issue persists.

Are the running and cab lights on a separate circuit or something with a fuse not in the box under the hood?

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[watersupply189]

I know on my 2016 the cab light fuse is under the hood.

Have you put a test light on that fuse to check for power?


2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

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[AK Bob]

I checked the wiring diagram for my 2014, and both the clearance lights and side marker lights are on fuse F79, a 15A fuse located in the underhood power distribution center located left front of the engine compartment.

I hope this helps.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit, and 50 Gallon auxiliary fuel tank.

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[mike.v.lanzoni]

I do have the F79 as well for clearance.

The fuse is good surrounding fuses are all good as well.

I don't have a test light, but I think I've gone through everything reasonably extensively.

Not sure if I need a dealer trip, but I would like to avoid that based on some of the "modifications" to the truck.

I also don't know anything about a BCM that needs to be reset or checked.

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[watersupply189]

I do have the F79 as well for clearance.

The fuse is good surrounding fuses are all good as well.

I don't have a test light, but I think I've gone through everything reasonably extensively.

Not sure if I need a dealer trip, but I would like to avoid that based on some of the "modifications" to the truck.

I also don't know anything about a BCM that needs to be reset or checked.

This is just a shot in the dark but try disconnecting both your batteries for about 30 min to see if maybe everything will reset.


2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

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[AK Bob]

Hopefully, the reset suggestion above will take care of it.

If it doesn’t, you will need to scan the BCM for trouble codes.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon auxiliary fuel tank.

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[ricky_bobby]

AlfaOBD is necessary if you don't have it - no need to go to the dealer -

I do find it odd you said everything worked quite well until you hooked a trailer up or am I not correct in that? I would see if something is failed in the trailer wiring -

There are 'rear LED lamps' option in AlfaOBD which should be enabled if you have not done so -

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