LED tail light bulb issue - long and complicated

[Weslsew]

Sorry in advance, this is going to be long, but I need some help understanding LED tail light bulbs. I purchased a set of 6 LED bulbs from ebay. I also purchased a solid state flasher and installed it. I did not use any resistors. I installed the LEDs in the driver’s side only for comparison testing, and they worked fine. Then, I installed the passenger side ones, and I began to have an issue when I hit the brakes – the display on my stock radio and my odometer would turn off. When I released the brake, they would come back on. Brake lights all worked fine. This did not happen when the tail lights were on and the brake was pressed.

Then, the issue stopped, however I noticed that the driver’s brake lights no longer worked. The driver’s tail lights still worked, and the passenger side was fully functional.

I removed the LED bulbs from the driver’s side, and I noticed that one had a bulge in the plastic base. I took it apart and discovered this. There was apparently a resistor and a diode on the inside, and the resistor had apparently burned and gotten hot enough to damage the housing and de-solder the leads from the bulb. The other driver’s bulb also had the resistor burned. My question is why?

I have learned that these LEDs have both the power for the tail lights and the power for the brake/flasher tied together.

Now, I’m confused on how the bi-filament effect is achieved. Either the tail circuit must provide a stepped down voltage to dimly light the LED, or the resistor on one of the LED’s leads must reduce to power to get the dim glow for the tail lights. I’m guessing the first, because with incandescent bulbs, the tail light circuit provides a dim glow on one filament, and the brake/flasher provides full power to brightly light the other filament.

If that is the case, and I think it is, the lead with the diode must go to the tail light circuit, which prevents a power backflow when the brake or blinkers are on. I’m not sure the purpose of the resistor on the lead for the brake/flasher circuit?

I’m thinking that my LEDs must have had the leads in the wrong positions, or the diodes must have been defective because it would seem that I was having some power backflow into my tail light circuit when the brake was pressed, thereby causing the issue with the radio display and odometer since they are tied in to the instrument panel illumination.

I’m starting to think that just the diodes were defective, because apparently when the resistors burned out, the brake circuit became open and that’s why the brake lights no longer lit. Maybe it was the extra current draw of backfeeding the tail light circuit that caused the resistors to overheat and burn? I can’t figure out what the purpose of the resistor is?

Now, I should be able to replace the diodes and the resistors (if necessary) and then be good to go? I don’t know what caused the diodes to fail, maybe just being cheap, ebay components? Another thought is that maybe the leads near the base of the bulb were touching because they are uninsulated, and caused the issue.

Thanks for any help or thoughts, I just want to run the LEDs because the rise time matches the 3rd brake light. I think the LED 3rd brake light looks so weird with the incandescent side brake lights. Not that I ever see it lol

 

[Huachipato]

The resistors are there to regulate the current. All LEDs need this because on their own they have no way to regulate the current that flows through them. All you need is a little voltage flowing the right directions and then it pretty much becomes a switch turned on (a short) without the resistor there to control the flow.

I would think that they would have a small resistor to allow for the bright lights (brake lights) to work and a big resistor to dim it down for just the tail lights to work. It is the current that determines the brightness with an LED, not the voltage. In this case the voltage applied will be the same for either. In the regular bulb the difference is the filament that gets lit - not the voltage that lights it. That seems to be how it is wired up since both Resistors are wired up to the same input. Even though they are wired together, the power still has to flow through one resistor or the other to get to the bulb.

I'm wondering if they were put in wrong or incorrectly wired to go to ground somehow.

 

[Weslsew]

I don’t think the LED bulbs can be installed incorrectly, because they have a polarity. They have both positives, one for tail light one for brake light, on the same end of the bulb. Therefore, they can only work one way. Now, the leads on the inside of the bulb housing can be connected to the wrong contact on the outside of the housing. Thoughts on whether this happened?





How does the car light incandescent bulbs dimly for tail lights? If not by lower voltage, there must be a resistor inside the car, because I believe with incandescent bulbs with two filaments, both filaments are identical. That’s why you can install these bulbs either direction and they still function correctly. I guess I can find the answer to this with a voltmeter. This would also make sense as to why there is only a resistor on the brake lead inside the LED bulb, since there is already one in the car for the tail light circuit.

 

[Huachipato]

The stock bulbs are dual filament bulbs. The filaments are different. You can measure the resistance on the old school bulbs if you want and you should find that they are giving you two different measurements of resistance. The lower the resistance, the higher the current, the brighter the bulb should be.

So - I'm re-reading your plight - and I believe you are right - the diode should be there to block the reverse voltage. I don't know why I looked at it as if it was a smaller resistor.

I think they way it works is one lead has power straight through the diode and then to the bulb (Brake light). Assuming it has an internal resistor inside the bulb. The power coming in from the other side would have to flow through the big resistor and the internal resistor (restricting current flow and dimming the lights - for night driving tail lights) and the diode would prevent the current back flow. The interesting thing to me - is you would think it would have 2 diodes (one on each lead) since it is essentially combining two circuits together when you hit the brakes (if my assumptions are correct).

It may just be that the resistor was defective or poorly rated for the job (not rated for the actual watts it was seeing) or it just overheated and burned that way. It doesn't look like there is much in the way of heat dissipation on that bulb.

 

[Kyle_KleinSS]

I had led front and rear bulbs from ebay. I wired in resistors and still had the same issues you are describing. I took them out and sent them back. Went to walmart and they sell led bulbs there. Said they have error codes or hyper flashed so I bought them. Work like a charm. More pricey than the ebay ones but they work great and dont cause my odometer and radio to flash. Also with the front in the turn signals were always illuminated telling me a bulb is out. That is no longer and issue either. Take out the ebay junk and go to walmart. The ones I got are made by pilot and work and look great.

 

[traktrbeam]

Hmmmm......May be stopping by Wal-Mart

 

[Weslsew]

I assumed the filaments in the incandescent bulbs were identical, that’s why you can install them in either direction, but I’ll test them and see.



The diode definitely has to go on the side of the tail light circuit. It is needed there to prevent current backflow from going back and messing with the instrument panel illumination. There is no need for a diode on the brake light circuit because when the brake lights or flashers are off, those switches are open and there is nothing on that circuit to draw current. Therefore, the lead with the resistor must be for the brake light circuit, and I can’t think of a reason it would be there unless it’s just for current regulation, and there is already a resistor on the tail light side of the circuit somewhere in the car. This is why it is my thinking that the diode failed, causing power to backflow in and mess with the instrument panel illumination when I pressed the brake pedal. The resistor on the brake light lead was limiting the current just enough to make the odometer and radio display do weird things, and then the extra current draw on that resistor overheated it. The question is why did the diodes fail? The diodes only cost pennies, so I think I’m going to replace them and see what happens.



I saw the Pilot ones on Amazon, but they were more than I cared to spend. I’ll swing by Walmart and see what they have.

 

[FromGTtoSVT]

LED bulbs in the tail lights are more trouble then they are worth IMHO. diminished out put and you need to splice in resistors, no thanks.

 

[Huachipato]

diodes (and LEDs) do not regulate current. They behave more like a back flow valve in that they only let the current and voltage to pass through in only one direction. They are more of a gate keeper in that sense. You need the resistor there to regulate the current.

In that design - I believe if they had put 2 diodes instead of just one (one side with just the diode and the other side with the diode and resistor) - then the issue may not have shown up at all. It would have essentially isolated both circuits from each other. You had the issue only when the brakes were applied - which makes sense (to me anyways) because the resistor alone cannot isolated the tail light circuit.

 

[Weslsew]

Okay, just did some testing. The incandescent bulbs are indeed two different filaments. The way the leads are, the tail light filament has the leads on the inside of the base, with one on the top and one on the bottom, on opposite ends. The brake light filament has the leads on the outside of the base. This is why you can flip it over and insert it either way, and it still functions properly.



I opened one of my still good LED bulbs, and the way it is set up, the resistor is on the inner set of leads (tail lights) and the diode is on the outer set of leads (brake lights). There is also a resistor on the inside of the LED cluster tower, so that is the one that regulates the current, regardless of which circuit is applying power.



The external resistor on the inside leads makes sense, as it is dimming down the tail lights. Why the diode is on the brake light lead though, I have no idea. It must be wrong. Maybe that’s why these were $1.50 from ebay.



I also learned how to test diodes with my multimeter, and the diodes on the two bulbs I showed you were open, hence why the brake lights no longer worked.



From what I have learned, I’m going to put a diode and resistor on the tail light side and see what happens. I guess I'll put a diode on the brake light circuit also, even though I don't think its needed.

 

[Huachipato]

The diodes should be there to isolate the circuits. Diodes are cheap - just make sure it is rated to handle more current than you will be pushing through it and you should be fine.

 

[Huachipato]

I just thought of something that might explain why your dash and radio (assuming it is stock) went "off" when you applied the brakes. I assume that when you say off, that it was just the display and the actual radio stayed running as normal.

My thought is that the tail lights circuit may be shared with other components - including maybe the instrument panel and radio lighting. My theory is that when you applied the brakes - the voltage flowed through the resistor and "tricked" the car into thinking the lights were on. As a result the car went into "night light" mode (I'm calling it that cause I don't know what else to call it but I think it explains my thought). So the odometer and radio dimmed as a result - however they were being fed power through your light bulb instead of your light switch. This would also explain why the resistor burnt out - you were pushing a whole lot more current through the resistor and burnt just that component out.

Now - in line with that theory - if you don't put the second diode to block the tail light current from feeding into the brakes circuit - I'd be interested to learn if your third brake light lights up dimly when you turn on the lights.

Anyways - just a theory. Might also be the reason why others with this issue cannot resolve it by simply adding a resistor. Instead of a resistor - if others used a diode it may correct the issue as well.

 

[Kyle_KleinSS]

I assumed the filaments in the incandescent bulbs were identical, that’s why you can install them in either direction, but I’ll test them and see.



The diode definitely has to go on the side of the tail light circuit. It is needed there to prevent current backflow from going back and messing with the instrument panel illumination. There is no need for a diode on the brake light circuit because when the brake lights or flashers are off, those switches are open and there is nothing on that circuit to draw current. Therefore, the lead with the resistor must be for the brake light circuit, and I can’t think of a reason it would be there unless it’s just for current regulation, and there is already a resistor on the tail light side of the circuit somewhere in the car. This is why it is my thinking that the diode failed, causing power to backflow in and mess with the instrument panel illumination when I pressed the brake pedal. The resistor on the brake light lead was limiting the current just enough to make the odometer and radio display do weird things, and then the extra current draw on that resistor overheated it. The question is why did the diodes fail? The diodes only cost pennies, so I think I’m going to replace them and see what happens.



I saw the Pilot ones on Amazon, but they were more than I cared to spend. I’ll swing by Walmart and see what they have.

Yea they were 15 bucks for 2 bulbs. I get a discount cause I work at the DC. Regardless, by the time I bought all my bulbs, the resistors, and the led flasher relay, it was cheaper to just buy the pilot bulbs. Plug and play, hassle free. Worth the extra money it would cost if you want leds. Just my 2 cents

 

[Weslsew]

So I added a IN4001 diode to each lead, and upgraded to a 1/2 watt 68 ohm resistor on the tail light circuit. These components were much much larger, but I was able to fit them into the bulb housing. Working perfectly so far...

 

[Weslsew]

I just thought of something that might explain why your dash and radio (assuming it is stock) went "off" when you applied the brakes. I assume that when you say off, that it was just the display and the actual radio stayed running as normal.

My thought is that the tail lights circuit may be shared with other components - including maybe the instrument panel and radio lighting. My theory is that when you applied the brakes - the voltage flowed through the resistor and "tricked" the car into thinking the lights were on. As a result the car went into "night light" mode (I'm calling it that cause I don't know what else to call it but I think it explains my thought). So the odometer and radio dimmed as a result - however they were being fed power through your light bulb instead of your light switch. This would also explain why the resistor burnt out - you were pushing a whole lot more current through the resistor and burnt just that component out.

Now - in line with that theory - if you don't put the second diode to block the tail light current from feeding into the brakes circuit - I'd be interested to learn if your third brake light lights up dimly when you turn on the lights.

Anyways - just a theory. Might also be the reason why others with this issue cannot resolve it by simply adding a resistor. Instead of a resistor - if others used a diode it may correct the issue as well.

Interesting, I think you might be right. I didn't want to take the chance with the third brake light, so I just went ahead and put a diode on the brake light lead for good measure. Thanks for your help!