Electrical experts weigh in: Why do LED taillights do this?

I replaced all the bulbs in my truck with LEDs (except for my headlights and the 3 bulbs in the A/C control and the OEM radio backlight).

When I press the brake pedal and the tail lights illuminate, the RIGHT turn signal indicator on the dash lights up about 20% brightness. The left turn signal indicator lights up about 5% - very faint.

Why does this happen? Brake lights are on a different circuit than turn signals.

Here's a photo - keep in mind that it makes it look like the right indicator is 100% on, but it's not.

 

Grounding back through the turn signal circuit .

They do share a common ground .

Myself I have had nothing but trouble with LED bulbs maybe with some time they will get better

The lights I have great luck with .

 

Maybe @mesojdm can explain he does own the LED taco

 

Cannot help you but I think it has something to do with resistance values of the LED bulbs.
They do not have the same resistance as regular incandescent bulbs and this does sometimes cause issues when swapping LEDs in things that were originally designed for regular bulbs
Resistors are usually added to solve the problem

 

I'm not positive, but I wonder if it could have to do with the electrical system being switched on the negative side of the circuits. Aren't most folks able to run LEDs without issue?? If so, I'd be checking all of the grounds.

 

To address the comments so far, load resistors are bullshit. I know how to modify the circuits to work with the lower power LEDs, I just haven’t figured out why this specific circuit is behaving like this.

All the LEDs in my truck work fine, there is just this side effect that is slightly annoying only because I want to understand why it is occuring.

yes, they may share a common ground, but power would not go back through the turn signal circuit when I have an LED in there because the D in LED is diode. These are one way streets for electricity. It does not flow backwards.

As for the “maybe sometime [LEDs] will get better” comment: at the time these trucks were made, LEDs were both prohibitively expensive AND had nowhere near the light output they do now. Also, vehicles (not just Toyota’s) were designed specifically for the power draws of incandescent bulbs. They saved money by designing the circuits “dumb” because that’s how manufacturing goes. Then when we put in LEDs, which use a fraction of the power, the original wiring and circuits of the truck get confused.

It’s not the LEDs fault and load resistors are the easy fix to make them behave like the incandescent bulbs the system was designed to handle.

Rant over. Any electrical experts out there with the answer?

 

Load resistor comment - agree, swapping incandescent for LED and then add the high power resistor is plain stupid.

Regarding LED - Diode comment it is not correct. The bulb is not just LED but polarity protection (reverse voltage on LED chip is very low, so if reverse 12 V would be applied to LED chip, it will blow) and current regulation circuits. They may let the current go "the other direction".

Do you have trailer adapter installed anywhere? If not, then I think you have a grounding problem (usually is).

To verify do simple diagnostic: remove the right rear turn signal bulb and see if the issue disappears. The second test would be just measuring voltage between ground on right tail lamp and battery negative pole. Anything more then 0.01V would be bad.

 

Yes, but nothing is plugged into it right now. This is another relic of the previous owner that was done poorly - just tapped into the driver side tail light wiring with those stupid plastic clamps. I've been meaning to pull the tail light out and clean that up / replace it with a better setup. Probably replace it with the Hopkins 43315.

 

Take it out. 99% this thing is leaking current to your blinker. It has to be connected to the right side too (for providing right blinker to the trailer).

 

When installing these LED bulbs are you changing your sockets as well??

Have you ruled out a leaking diode ??

 

I purchased all of my LED replacements from superbrightLEDs.com. I ordered the correct socketed replacements for each location and have not done anything more than remove the incandescent bulb and replaced it with the LED version.

I did solder in some high wattage resistors to the dome light LEDs to keep the 30 min auto-shutoff working on my 2003. Stupid load resisters.

No, I have not ruled out a leaking diode. I haven't gone to each of the LEDs and tested/verified that they are all good other than a illumination check every few weeks since I installed them 4 years ago.

 

I had a "leaking" LED but the symptom was obvious: every time I step on brakes my panel lid up. The culprit was "dual filament" Stop/tail light LED bulb - when I step on brake the LED was leaking the voltage to tail light circuit.

However Turn signal and Brake (or tail) circuits are totally separated. Only common point is ground on tail light. If ground is not connected to battery negative, than all different gremlins may come out. However it would be more consistent across. With just right turn signal showing up it is very possible that trailer converter (which is common point between brake and turn lights) might leak something.

 

First question I was going to ask is if you have a trailer harness. Just like Rysium said, if you remove it, you will most likely solve your issue. It wasn't apparent before with the incandescent bulbs because they take more amperage to illuminate.

If the trailer harness doesn't solve your problem, the next question I would ask is "do you have aftermarket taillight housings?". All taillight housings are not created equal. This stems from the older 95-00 tail lights being wired different for grounds. When manufacturers started producing 01-04 aftermarket lights, they didn't always change the wiring to match 01-04.

 

I install load resistors (hyper flash fix) and also run a new chassis ground- but I also ditched the OEM setup as you can see in the junker build.


https://www.tacomaworld.com/threads/junker-build.574266/

Here's the resistors:

$10 50W 6Ohm LED Load Resistors for LED Turn Signal Lights or LED License Plate Lights (Fix Hyper Flash, Warning Cancellor)

https://www.amazon.com/Resistors-Signal-License-Warning-Cancellor-x/dp/B004EDF8HY