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Lighting Forum
Angel Eyes, DDEs, lighted rings, Clear Turn Signals, LEDs, Xenon, HID, or Bi-Xenon. If it lights up and you want to discuss it, post here!

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Old 04-17-2013, 02:17 AM   #1
Bimmerboye46
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Exclamation Tail Light Alert (Aftmkt L.E.D.)

2001 325i sport

I installed aftermarket LED tail lights with two resistors on each lamp, I haven't had any problems until now.


LED bulbs pass a lower current compared to a normal OEM lamp. W/O resistors the car would think the tail lights were burnt out. The resistors purpose are to slow down the current so the car can recognize the lights. (from my understanding)


Recently this F^*KING thing has been coming on/off.



My question is: if it were a specific resistor at fault (fried or bad connection), wouldn't only the lamp side at fault light up? Why does it turn on/off randomly all of a sudden? Bad ground to all of them? What causes this?! please help
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Old 04-17-2013, 02:25 AM   #2
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What brand?
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Old 04-17-2013, 02:30 AM   #3
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I presume the resistors are in parallel with the LED lights. The function of the resistors is to add load to fool the computer into thinking that the bulbs are healthy.

My guess would be that the resistors are burned out. I think the average bulb is about 20W. You probably need quite beefy resistors.

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Old 04-17-2013, 02:36 AM   #4
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What brand?
I cannot recall the brand of aftermarket tail lights. My cousin installed them when he owned the car before me. Ebay Im sure...
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Old 04-17-2013, 02:38 AM   #5
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I presume the resistors are in parallel with the LED lights. The function of the resistors is to add load to fool the computer into thinking that the bulbs are healthy.

My guess would be that the resistors are burned out. I think the average bulb is about 20W. You probably need quite beefy resistors.

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Thanks for the reply! But I wouldn't think both sides (L/R) would burn out at the same time! That's what confuses me...
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Old 04-17-2013, 02:40 AM   #6
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Well i just ordered some new tail lights. i'll probably sell my perfectly working old ones if you're interested. theyre eagle eye LEDs. they look fantastic and no burnt out leds or error lights or fading of any kind. mint cond.
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Old 04-17-2013, 02:45 AM   #7
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Well i just ordered some new tail lights. i'll probably sell my perfectly working old ones if you're interested. theyre eagle eye LEDs. they look fantastic and no burnt out leds or error lights or fading of any kind. mint cond.
1. Will they fit my 01 325i?
2. Do they have built in resistors?
3. How old?
4. How $?

...dammit mango im trying to fix these not spend money on new ones! lol, i appreciate the offer and might consider if i cant get these working. I think these are eagle eyes as well to be honest.
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Old 04-17-2013, 09:32 AM   #8
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Are the lights working? Or are they working but the dash display says they're burned out?

Or are they completely not working?

What value and how big are the resistors.

Reason I am asking....I am assuming these lights are drop in replacements you just connect to the loom and they work? I.e. the normal 12V is used.

A resistor, for a single naked LED, is used to limit the current to about 30mA. For 12V, the value would be typically 820 Ohms.

In an engineered solution, all the dropping resistors would be in the electronics of the light cluster, so you wouldn't have to worry about that.

I would guess the cluster would use 100 - 200 mA for the turn and stop signals, and maybe half that for the tail lights.

The globes would use 12 / 20 = 600mA. You can measure the currents that the Led cluster is using, and then calculate what resistance you need to make up the missing currents you need to fool the computer. ...

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Old 04-17-2013, 09:52 AM   #9
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Cont...

So for turn and stop, say you measured 200mA. Maybe the computer would be happy with 500. So you need an extra 300. You need a resistor of value 12 / 0.3 = 40 Ohms. The neatest value is 39 Ohms. The power rating would be I^2R, or 0.3 x 0.3 x 39 = 3.5 Watts. So a 39 Ohm, 5 watt resistor would work.

Note this would be for each light. You can leave the ones that don't activate the warnings...

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Old 04-17-2013, 10:26 AM   #10
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Cont...

So for turn and stop, say you measured 200mA. Maybe the computer would be happy with 500. So you need an extra 300. You need a resistor of value 12 / 0.3 = 40 Ohms. The neatest value is 39 Ohms. The power rating would be I^2R, or 0.3 x 0.3 x 39 = 3.5 Watts. So a 39 Ohm, 5 watt resistor would work.

Note this would be for each light. You can leave the ones that don't activate the warnings...

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To be honest I don't know what size resistors are being used but they've been working fine for years until now.

Lights still work just fine, the computer thinks they're burnt. Off/on. Usually goes away for a bit if I turn the car off.
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Old 04-17-2013, 11:01 AM   #11
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Are your license plate lights working?
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Old 04-17-2013, 12:00 PM   #12
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I have taken one license plate lamp out to install a rear view camera. The camera was equipt with a license light to compensate for the missing lamp. The camera light worked for the first 10min after install but when out. The other side (original license plate lamp) still works. I've had it installed like this for month an never had an issue. You think it could be picking up on tht short?
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Old 04-17-2013, 12:35 PM   #13
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Are you sure the car tells you if license lamps are burnt or not?
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Old 04-17-2013, 12:47 PM   #14
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That is likely your problem. It will indicate both tail lamps out. I had a similar problem that ended up being broken wires in the trunk wire loom.

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Old 04-17-2013, 01:57 PM   #15
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That is likely your problem. It will indicate both tail lamps out. I had a similar problem that ended up being broken wires in the trunk wire loom.
damn... I wonder why it shows up now instead of right after install. Thanks for sharing. Ill try to re route that before ordering new resistors.
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Old 04-17-2013, 02:15 PM   #16
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I find even that weird because the warning light turns on when I press on my brakes (headlights off).
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Old 04-17-2013, 03:34 PM   #17
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That's a different story then. Mine would show fault when I would turn the lights on.
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Old 04-25-2013, 04:49 PM   #18
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I bought 4X new 25w load resistors to match what was installed before. I know you T tap a (+ brake wire) & tap into a (- ground) with the other.

My problem is each 25w resistor has 4 wires rather than 2!

I twisted the two wires from one side of the resistor together and tapped into a (-). Then did the same with the 2 wires from the other side of the resistor but tapped into the (+) brake wire. It was incorrect because my indicator light is still present!

Any ideas what to do with the 2 wires on each side of resistor. They do not seem up be labeled differently than each other!
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