LED Tail Lights

Submitted: Monday, Jan 23, 2006 at 19:18
ThreadID: 30030 Views:2310 Replies:6 FollowUps:2
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Anybody know the secret of correctly connecting LED tail / stop / indicator lights. The guys installing my tray to my cab chassie originally wired them. However have discovered by accident that when turning on tail lights (parkers) the stop lights also come on. Have checked wiring, also light unit, and all is fine - till fully connected up. When you put test light across stop light when parker is on it reverts to normal?????? Has anybody had the same problem. I am thinking a diode or resister has to be installed across the stop light. Helpppppp!

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Reply By: Ken - Monday, Jan 23, 2006 at 19:54

Monday, Jan 23, 2006 at 19:54
Gary, check the earth on the lights. Poor earthing can play strange tricks with the lights such as all lights blink with the flashers, stop & tail come on together when braking etc. Probably nothing wrong with the LED lamp assemblies just a poor earth.

AnswerID: 150399

Reply By: Member - David 0- Monday, Jan 23, 2006 at 20:31

Monday, Jan 23, 2006 at 20:31
I am no expert but for flashers, sometimes the resitance of the led's is too low for the system to work properly. Adding resistance helps.
AnswerID: 150413

Reply By: Eddy - Monday, Jan 23, 2006 at 20:41

Monday, Jan 23, 2006 at 20:41
Is ths one side or both sides?

Make a difference to the answer.
AnswerID: 150419

Reply By: Member - Gary W (QLD) - Monday, Jan 23, 2006 at 20:48

Monday, Jan 23, 2006 at 20:48
Both sides - however by placing a test lamp (bulb) across 1 side it fixes both sides if that makes any difference. We found the problem after installing a cruise control. When you touch the brakes the control turns off ie goes into neutral. It all worked fine until during a shower of rain I turned on the lights and the control "dropped out". Had the control checked and thats when they found - by turning on the lights the brake light came on - so the cruise stops. Weird!
AnswerID: 150420

Reply By: Lone Wolf - Monday, Jan 23, 2006 at 21:34

Monday, Jan 23, 2006 at 21:34
Okay, I'll bite, but here's the thing... I'm NOT an auto electrician, or electrician full stop.

Digital electronics has some major differences than analogue, and it is sometimes a pain to get them to co-operate.

Now, I'm guessing, that with the advent of having your cruise control fitted, there is now a SMALL inherent current turned ON at all times, to sense if the brake pedal has been depressed.

Now, old logic would suggest that if the brake pedal was depressed, then the current would go from OFF to ON, therefore knocking out the cruise control. Digital logic would suggest, that you have a SMALL residual current ON at all times, waiting to be turned OFF by application of the brake pedal, which is by far a much SAFER way of monitoring.... no current....turn the system off.

So, this small monitoring current, which would simply be diverted when the brake pedal is depressed, by way of path of least resistance, is possibly the culprit, because traditionally, LED's only require a few volts to work, and are subject to voltage drops.

As I said, I'm just shooting in the dark here, but it fits with your explanation.


AnswerID: 150433

Follow Up By: Eddy - Monday, Jan 23, 2006 at 21:48

Monday, Jan 23, 2006 at 21:48
Try disconecting each side at a time & see if the problem goes away.

These units have diodes in them to stop back feeding from one circuit to the other (ie. stop to tail ) and 1 one side may have a biown one.

Hope this helps.

FollowupID: 403882

Follow Up By: Member - Gary W (QLD) - Tuesday, Jan 24, 2006 at 11:33

Tuesday, Jan 24, 2006 at 11:33
Thanks Lone Wolf - you're spot on!
Contacted cruise control guys and by fitting 100 ohm 5 watt resistor across brake light circuit in "fixs" monitoring voltage/current and now all is sweet.

Thanks for your advice.
FollowupID: 404000

Reply By: Member - Howard (ACT) - Monday, Jan 23, 2006 at 22:07

Monday, Jan 23, 2006 at 22:07
I'm not an auto electrician but the young bloke put LED lights on the tonka truck tray he built for the Hilux.He soldered in a festoon bulb before each led light(hidden in tray frame). apparently this provides the necessary resistance.
all I know is the lights work ok
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AnswerID: 150449

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