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So, installed a couple new LED 3157 tail lights with the resistors. All came as a kit. With car key in "ON" position everything works as should. Installed resistors to resolve the expected fast-flash issue.
Put everything back together and went for a drive. When the car is running, I get fast flashing with and without running lights on. With car not running, no fast flash...
Ideas? Suggestions? I did not note the spec of the supplied resistor sets. Is there a recommended spec anyone might suggest? '07 GXP
Cheers,
Allan
#practicesolsticedistancing
 

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So, installed a couple new LED 3157 tail lights with the resistors. All came as a kit. With car key in "ON" position everything works as should. Installed resistors to resolve the expected fast-flash issue.
Put everything back together and went for a drive. When the car is running, I get fast flashing with and without running lights on. With car not running, no fast flash...
Ideas? Suggestions? I did not note the spec of the supplied resistor sets. Is there a recommended spec anyone might suggest? '07 GXP
Cheers,
Allan
#practicesolsticedistancing
You probably need two resistors on each side. The difference between engine running and not is likely to be the difference in the 12V battery voltage and the 14.4V generator voltage.
 

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Discussion Starter #3
You probably need two resistors on each side. The difference between engine running and not is likely to be the difference in the 12V battery voltage and the 14.4V generator voltage.
Valid observation. At least a full volt between "ON" and running.
Thanks!
 

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Discussion Starter #6
AND, be very careful where you mount the resistors; they get VERY hot

Bill
Roger that. Noticed it right away. I wired the resistor so it would hang in the 1/4 panel cavity not touching anything at all.
 

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Roger that. Noticed it right away. I wired the resistor so it would hang in the 1/4 panel cavity not touching anything at all.
I bought mine from Amazon. 50w 6ohm. they worked fine. Mounted them to a metal part of the frame for additional heat sink. four resistors for about $8.00
 

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You probably need two resistors on each side. The difference between engine running and not is likely to be the difference in the 12V battery voltage and the 14.4V generator voltage.
From personal experience I would expect the opposite. I found that it's current draw that's detected and when I didn't have enough (i.e. resistor values too high) the lights would hyperflash when on the battery only (lower voltage) but work fine when the engine was on and charging.

So this situation is very puzzling. The only thing I can think is that the LEDs have active controllers that draw less current when the voltage is lower (maybe). In any case, as said above, it would be good to try more resistors in parallel or replacement with lower resistance values. The usual value is 6ohms but I would've thought that's what came with the LEDs in the first place. @Allan do you have LEDs in the front turns too? If so, do they have resistors in parallel as well? Note that the BCM 'measures' the current for both front and rear turns as a parallel set. So you can add your load resistors in either place and it will cover both.
 

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I used 6ohm resistors in front and back and they worked OK. Didn't know I didn't need to. However, I think you are right. If they still hyperflash, you need resistors with a lower resistance value.
 

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From personal experience I would expect the opposite. I found that it's current draw that's detected and when I didn't have enough (i.e. resistor values too high) the lights would hyperflash when on the battery only (lower voltage) but work fine when the engine was on and charging. ..........
I agree that is certainly the more logical result, but the only electrical difference between engine running or not is the voltage, and the cause of hyperflash is low current. My thought was that why wasn't as important as what at this moment, and throwing an extra resistor at it is fairly simple.

Maybe the BCM compensates for voltage? That sounds crazy even to me.
 

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From personal experience I would expect the opposite. I found that it's current draw that's detected and when I didn't have enough (i.e. resistor values too high) the lights would hyperflash when on the battery only (lower voltage) but work fine when the engine was on and charging.
I'm pretty sure he meant to put them in parallel (to double the current), not in series (to halve the current).
 

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I'm pretty sure he meant to put them in parallel (to double the current), not in series (to halve the current).
I did, but I think TS understood that. He is correct that the higher voltage through the same resistance will yield higher current and should not result in hyperflash with the engine running if it doesn't happen when the engine is off.

This case is definitely odd.
 

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Discussion Starter #13
So, I was an idiot with conflicting info. PROPER hook up Black & Yellow on the left light. Black & Green on the right. I ended up using Sylvania resistors. They are bigger than the unmarked ones that came with the kit. now I'm happy. thanks for the input. Pretty routine mod with the correct info! Cheers.
 

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Glad it worked out, and you provided us with something to discuss. Wins all around, I would say.
 

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Yeah, but my scalp is now raw with all the scratching! :D
 
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