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United Pacific LED taillight problem

Jon from Wexford, Pennsylvania visited my LED site and asked this question which I am unable to answer. Could someone help? Thanks guys

-- Leddie host of fun-led-light.com

"Purchased LED taillight units for '31 Model A ford (12volt). I bought three units so I could fabricate a matching 3rd brake light for the rear window. The lens/light units are made with upper and lower sections which are wired together to work as one. The turn signals are not part of the system. After installing them I found that the park lights work the way they should and the brake lights also. What I noticed was that with all switches off, there are three LEDs in the lower section of all three lights which glow dimly....The same three on each of the lights. All the other LEDs are off. How or why would these be lit with the switches controling them open? The United Pacific Company could offer no answers. Is this anything you've seen before? Thank you for any information you might provide."

Reply to
Leddie
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Just a guess: First of all, does this vehicle feed +12V battery to the + side of the brake lights at all times and ground the brake - to illuminate the lights?

If so, I'd look for a sneak circuit that allows a small current to flow from the brake light - side to ground. Something like a car alarm would do it.

I'm guessing that the 3 LEDs are used as crude voltage references in a regulator circuit that drives the remaining LEDs. The forward voltage across an LED is roughly constant for a wide current range. The LEDs in each light are broken up into 3 groups with one regulator (and LED) for each. The sneak circuit current is sufficient to cause these three to illuminate dimly, but not enough to turn on the others controlled by the regulator circuits.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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If Bill gates had a dime for every windows machine that crashed...
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Reply to
Paul Hovnanian P.E.

Thanks Paul, much appreciated. I asked Jon to reply so we know if this is what he experiences. Am featuring your response on FLL also -- Leddie

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Reply to
Leddie

Thanks Paul, much appreciated. Posted your reply for Jon on FLL also, see how this may help . -- Leddie

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Reply to
Leddie

Thanks Paul, much appreciated. Posted your reply for Jon on FLL also, see how this may help . -- Leddie

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Reply to
Leddie

Jon wrote back saying "Paul is exactly right. The circuit is designed just that way." Thanks Paul. He wrote a bit more about what he unearthed and I feature it at the thread

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Thanks again -- Leddie

Reply to
Leddie

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