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LED Tail Light Resistor


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Last year I made tail light boxes with a set of S/T/T LED lights.

 

 

Over the past couple of months I noticed the passenger tail light had gone out and now the driver side is no longer working, but the brake/turn signals still work. Today I got a chance to look into how these things are wired. I found this when I opened up the pseudo protective wrapping in the wiring.

 

 

You can see at the light plug in it is a two wire hook up. The black wire controls both the tail light and stop/turn functions. Following the wiring from there you can see where the wiring splits for stop/turn (red) and tail (brown with resistor).

 

I've traced that the tail light wiring is good up to the resistor thing. After the resistor - no more power. I'm pretty sure the resistor has gone bad.

 

Here is a close up of the resistor.

 

 

Can anybody tell from these numbers what I need to replace these with? Also, where would I find some that are a little better quality than what these came with?

 

Thanks,

Willy

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I'm not running LED's in the MJ yet, but on my XJ I had a similar problem. I ended up needing a different flasher. The LED's didn't pull enough load to make the flasher work. Once I swapped in a different flasher (electronic) I've not had any problems to date (been running them for 3+ years now).

 

Don't know if it'll help or even related, but I got mine from Autozone. Part number EL12 (2 prong).

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You can see at the light plug in it is a two wire hook up. The black wire controls both the tail light and stop/turn functions. Following the wiring from there you can see where the wiring splits for stop/turn (red) and tail (brown with resistor).

 

I've traced that the tail light wiring is good up to the resistor thing. After the resistor - no more power. I'm pretty sure the resistor has gone bad.

Do you have a wiring diagram? I don't think you understand what you're working with. There is no way one wire can "control" both taillights and stop and turn functions. That's the ground wire. The other wires are the power wires, and THEY are what control the lights.

 

Are you certain that little thingie is a resistor? I have no idea how LEDs work, but I don't see any need for a resistor. Could that be a diode? To ensure that current only flows one way?

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I'm not running LED's in the MJ yet, but on my XJ I had a similar problem. I ended up needing a different flasher. The LED's didn't pull enough load to make the flasher work. Once I swapped in a different flasher (electronic) I've not had any problems to date (been running them for 3+ years now).

 

Don't know if it'll help or even related, but I got mine from Autozone. Part number EL12 (2 prong).

 

That is a completely different issue. The flasher works fine.

 

You can see at the light plug in it is a two wire hook up. The black wire controls both the tail light and stop/turn functions. Following the wiring from there you can see where the wiring splits for stop/turn (red) and tail (brown with resistor).

 

I've traced that the tail light wiring is good up to the resistor thing. After the resistor - no more power. I'm pretty sure the resistor has gone bad.

Do you have a wiring diagram? I don't think you understand what you're working with. There is no way one wire can "control" both taillights and stop and turn functions. That's the ground wire. The other wires are the power wires, and THEY are what control the lights.

 

Are you certain that little thingie is a resistor? I have no idea how LEDs work, but I don't see any need for a resistor. Could that be a diode? To ensure that current only flows one way?

 

Yes, the black wire at the plug in controls both the stop/turn and tail functions. Take a look at the second picture. Ground is the white wire. Red is the stop/turn. Brown is the tail. Notice how the red and brown both become the black wire. The resistor limits the amount of power going to the lights only partially illuminating them for the tail lights. When the non-restricted red wire receives current the lights receive full power and fully illuminate.

 

That is a 360 ohm 5 Watt wire wound ceramic covered resistor. Can be picked up at any Radio Shack, Electronic supply or your local ham operator or TV repairman.

 

Thanks, that's what I was looking for. Are there any that are better quality or are they all about the same?

 

Thanks,

Willy

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Leds' are very voltage sensitive. Exceed their voltage rating by even the smallest percentage and their current draw goes out of sight, wiping them out instantly. Most Leds for auto use are rated at 16V well within the automotive max of 15V max, 14.2 ave. I believe the resistor is to supply a load for the flasher altho you said the flasher worked ok B4. Would really need a schematic of the circuit to fully understand it. Also suggest you check the resistor to insure it is in fact bad. Set the ohmeter scale to 1K, common on most meters. The meter should read between 336 to 394ohms, for a .5 precision res. And for the purists B4 U jump on my figures, I'm doing this in my head. No calculator.

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The resistors are added to the LEDs to supply a resistive load so the flasher will work. The flasher needs a finite amount of current so it's contacts will heat up and open/close. All flashers are different; they are primitive. Sometimes replacing your incandescent blinker bulbs with LEDs works fine w/o the load resistors, sometimes the LEDs won't flash, sometimes thay flash too fast, and sometimes they just turn on. Even though your flasher may be making/breaking it doesn't mean the LEDs will fire. Lead has the easiest solution; get a 2-prong electronic flasher and dump the resistors. The electronic flashers have a much broader range of operability than mechanical flashers, and it should work fine for you. I've just been through all this with my motorcycle......

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Looks to me that in this particular setup, the resistor (and yes, it's definitely a resistor, described correctly by jimoshel) is a voltage dropping resistor for dimming the LEDs when they are used as tail (you can dim an LED with a voltage dropping resistor, and the 360 ohms wouldn't drop it by very much in series with an LED), and the red wire gives them a shot of the full 12-14v via either the brake switch or the turn siganl flasher. reson46 did say that the brake/turn signals are still working, which to me indicates that the resistor is DOA. That resistor is a 5 watt, so if you can find one, get yourself a 10 watt. Eagle, if you have a parallel circuit, one side through the resistor and the other switched, you can have one wire controlling the same LEDs to make them fucntion as either tail or brake/signal lights. Then you'd need only the one ground.

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I am no electrical expert and I know there are issues with some LEDs not drawing enough current to make the flashers work. But, I fail to see how that has anything to do with the problem I am having. I am not having problems with my turn signals (red wire). The turn signals and brake lights work fine. It is the tail light function that is no longer working. The tail lights do not use the the turn signal flasher.

 

Jim,

Thanks for the numbers. Tomorrow I'll play around with the meter just to verify the resistor is bad. So far I've just checked it with a test light.

 

What do the OHMs measure in all of this? I stopped by RadioShack this afternoon. The only 5 watt resistor they had was .47 OHM. I'm guessing this won't work for what I need?

 

Thanks,

Willy

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Looks to me that in this particular setup, the resistor (and yes, it's definitely a resistor, described correctly by jimoshel) is a voltage dropping resistor for dimming the LEDs when they are used as tail (you can dim an LED with a voltage dropping resistor, and the 360 ohms wouldn't drop it by very much in series with an LED), and the red wire gives them a shot of the full 12-14v via either the brake switch or the turn siganl flasher. reson46 did say that the brake/turn signals are still working, which to me indicates that the resistor is DOA. That resistor is a 5 watt, so if you can find one, get yourself a 10 watt.

 

Thanks, I'll see if I can find a 10 watt. Are the OHMs important for what I'm doing?

 

Thanks,

Willy

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Radio shack doesn't carry anywhere near the electrical components that it used to carry. They have nearly gotten completely out of the business of electronic components and concentrated on phones TVs boom boxes and such. I have a good freind who just retired from RS management, and they're hurtin' real bad with this economic downturn. Might have to go to Graylock online or some such place.

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reson46 did say that the brake/turn signals are still working, which to me indicates that the resistor is DOA.

 

Crap - I missed that. Thought his turn signals were out. :grrrr:

 

However, if an LED has smoked a 5W resistor, and some of the LEDs themselves have burned up, something is wrong. Load resistors are normally 40-80 ohms, 1 or 2 watts. The typical LED only draws 30-50 milliamps. I think the load resistors are sized too large.

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Reading all of the answers I also believe the resistor to be dead. I would still check it tho just for the heck of it. If in fact the resistor is to control the brightness of the LED then the higher the resistance the dimmer the LED. The lower the resistance the brighter the LED and the less difference in illumination between stop and tail. In that case you could probably use any value between 250 to 400 ohms. If you can't find anything check the auto supply.Some of the old style ignition dropping resistors and alternator field coil resistors might work. A walk thru the JY should furnish a bunch of them. If you still can't find one let me know. I only got a couple hundred of them. Jim

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However, if an LED has smoked a 5W resistor, and some of the LEDs themselves have burned up, something is wrong. Load resistors are normally 40-80 ohms, 1 or 2 watts. The typical LED only draws 30-50 milliamps. I think the load resistors are sized too large.

 

 

A lot of the newer super bright LED arrays used in vehicle lighting are more like 300-700 milliamps, which would put them around 3.5 to 8 watts or more. He didn't mention any of the LEDs being fried. I agree that the resistor could be in a range somewhere around 360 ohms, but was saying the ohms were important in response to his question after finding a .47 ohm resistor at RS. That would definitely not do the job.

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Okay, just a quick check got me here... http://www.surplussales.com/resistors/W ... -3999.html They have a 360 ohm, 5% tolerance, 30 watt wirewound for $5/ea. (the first 360 ohm listed) Ought to do the job. I'd suggest that you encase it in heat-shrihk tubing , then seal the ends with silicone or something to help protect it from the elements.

 

I'm definitely going to try to seal it as best as possible. The tubing that came with these lights offered no protection from the elements. It's no surprise the resistors went bad now that I've opened it up. :roll:

 

However, if an LED has smoked a 5W resistor, and some of the LEDs themselves have burned up, something is wrong. Load resistors are normally 40-80 ohms, 1 or 2 watts. The typical LED only draws 30-50 milliamps. I think the load resistors are sized too large.

 

 

A lot of the newer super bright LED arrays used in vehicle lighting are more like 300-700 milliamps, which would put them around 3.5 to 8 watts or more. He didn't mention any of the LEDs being fried. I agree that the resistor could be in a range somewhere around 360 ohms, but was saying the ohms were important in response to his question after finding a .47 ohm resistor at RS. That would definitely not do the job.

 

I don't think any of the LEDs are bad. I didn't specifically check each one, but it still looked like it was putting out as much light as normal.

 

Reading all of the answers I also believe the resistor to be dead. I would still check it tho just for the heck of it. If in fact the resistor is to control the brightness of the LED then the higher the resistance the dimmer the LED. The lower the resistance the brighter the LED and the less difference in illumination between stop and tail. In that case you could probably use any value between 250 to 400 ohms. If you can't find anything check the auto supply.Some of the old style ignition dropping resistors and alternator field coil resistors might work. A walk thru the JY should furnish a bunch of them. If you still can't find one let me know. I only got a couple hundred of them. Jim

 

Excuse my ignorance, but is the resistance measured in OHMs? A 250 OHM resistor would provide less resistance and produce a brighter illumination than a 400 OHM resistor?

 

A Google search did return some results for 360 OHM 5 watt resistors. I'll go through them to see what I can find.

 

Thanks,

Willy

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Excuse my ignorance, but is the resistance measured in OHMs? A 250 OHM resistor would provide less resistance and produce a brighter illumination than a 400 OHM resistor?

 

Yes, you are correct. That's why I had answered that the ohms was important. The range of resistance that you and jimoshel have mentioned should work fine, a little brighter @250 ohms, or a little dimmer @400 ohms. The resistor's wattage is important, too. If your LEDs are pulling, say 5 watts total per array, then you could theoretically use a resistor with a minimum 5 watts. Practically speaking, using this absolute minimum power handlng capability (5 watts), expect it to fail after awhile. It would be better to use a resistor with a power handling capability twice what was necessary, which is why I suggested you use a 10 watt resistor. The 30 watt that I found on the website that I pointed out is a little overkill, but if properly protected, should never burn out due to the current draw of the LED array.

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A lot of the newer super bright LED arrays used in vehicle lighting are more like 300-700 milliamps, which would put them around 3.5 to 8 watts or more. He didn't mention any of the LEDs being fried. I agree that the resistor could be in a range somewhere around 360 ohms, but was saying the ohms were important in response to his question after finding a .47 ohm resistor at RS. That would definitely not do the job.

 

Willy states that he used S/T/T LED lights and the tail light was out due to the blown load resistor. S/T/T makes these two round lamps:

 

4" Round Stop-Turn-Tail Light, 10 LED Red (5624110)

2" Round Marker Light, 1 LED Red (5622101)

 

I suspect he's got the 2" round unit, but even if he has the 4" 10 LED array tail lamp, it should typically draw no more than 60 milliamps. I still think the load resistors are sized too large for this LED application.

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