LED tail light swap not working properly

Tiny
QUARTETBARI
  • MEMBER
  • 2004 DODGE RAM
  • 4.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 1,000 MILES
Just swapped the old rear tail light assemblies for new C-bar LED tail lights (and 3rd brake/cargo light) as part of my custom restoration. After installation, my rear blinkers started hyper flashing, brake lights didn’t work (they “strobed” when I pressed the brakes) and the “lamp out” message appeared on the dash. Running lights work fine as does the 3rd light.

After some research I installed 8ohm/50w resistors grounded to the body and connected to the blinker wire on each rear tail light. I tested everything with the key on “acc” and the problem appeared to be solved. That is until I cranked the truck up.

With the truck running, as soon as I press the brake, the “lamp out” lights up, brakes strobe when brake is applied, and rear blinkers don’t work. Weird thing is, the front (standard bulb) blinkers work with their normal cadence. Also, the 3rd light works properly.

I’ve read that this generation of truck, particularly 02-05, is very persnickety when it comes to electrical changes.

I’m at a loss as to what to try next. I love the look of these tail lights but need them to work properly.

Any suggestions?
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Friday, January 15th, 2021 AT 6:12 AM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I need to understand something. You replaced the rear lights but mentioned the fronts are still the original incandescent type bulbs. Is that correct?

If it is, let me know. The wiring between the front and rear are tied together and likely the problem. Are you planning to replace the fronts as well?

Let me know.

Joe
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
QUARTETBARI
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Hi Joe and thanks for the quick weekend reply!

You are correct, fronts are still incandescent. My plan is to change the front headlight assemblies out to C-bar LED headlights with sequential LED blinkers. Just haven’t pulled the trigger because they are almost $400.00 for the pair and the tail light issue has me a little spooked.

Anxious to hear your thoughts!

Thanks,
Chris
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,005 POSTS
Chris,

I have to be honest when mixing LED and traditional lighting, there are always problems simply due to the voltage variations. I don't want you to spend a lot to check. However, can you get an inexpensive LED and wire it in one section at a time to see if it then works?

Also, you haven't changed any of the wiring paths, correct?

Joe
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
QUARTETBARI
  • MEMBER
  • 5 POSTS
I could easily pick up LED blinker bulbs for the front. If I do that, I assume I will need to install resistors up front, too? I already have the resistors.

Since the new rear assemblies have LED brake lights, too, do I need to install resistors on the rear brake wires?

I haven’t made any changes to the existing wiring rear light wiring other than installing the resistors. I’ve attached a couple of pics so you can see how it’s wired. You’ll notice that I added a jumper across the ground on the driver’s side. I had a poor connection on this side.
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Try an LED first before we start making changes. We need to see how things change. This isn't one from a manual. LOL Let me know.

Let me know what you find.

Joe
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
QUARTETBARI
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  • 5 POSTS
Joe,

I swapped the front incandescent blinker bulbs to LEDs. Got rapid flash again so I installed resistors (6Ohm/50watt) at each front blinker. That settled the rapid flash but didn’t do anything for the “lamp out” or strobing at the rear brakes.

It did get me thinking and I noticed a pattern to the rear brake strobing issue. It started strobing and displaying the “lamp out” error after I left off the brake. Letting off the brake created a wattage drop that the computer detected as a bulb out. On stock taillights, this model truck has 2 bulbs on each side drawing energy when the brakes are pressed. So I added an 8Ohm/50watt resistor to each rear brake light wire.

Voila! No strobing tail lights and no more “bulb out” warning light. Going to test drive it tomorrow to make sure, but I put it through multiple tests (running and not) in the garage and it never failed.

I’ll let you know how it goes!
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Tuesday, February 9th, 2021 AT 5:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

That's good news. I can't tell you how often people have trouble changing the lights.

Regardless, I'm glad it's fixed. Please feel free to let me know if you run into any other trouble. Also, please feel free to come back in the future if you need anything. You're always welcome.

Take care,
Joe
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Tuesday, February 9th, 2021 AT 5:49 PM

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