Simple Circuit Help- Automotive Lighting Circuit

Mar 16, 2007 4 Replies

Hi All, I'm hoping someone can help me, i have what is probably a simple problem-



My car (Mitsubishi) has a dual filament stop/tail light for each of the rear lights (12v 5/21w), and a 3rd LED highlevel brake light.



Incase your not familar with this setup due to this being an international newsgroup and i'm in the UK, when you turn your headlights on, the 'tail' light filament of the bulb illuminates (5w) and illuminates the red section of the rear cluster. When you press the brake pedal, the 'stop' light filament of the bulb illuminates (21w) and the red section of the rear cluster illminates brighter, also the red LED brake light illminates.



I wish to replace the stop/tail light bulbs with LED items, these i have bought and fitted, however they give the following issue-



They work fine in the cluster for stop/tail operations, but when in the tail light only (Lights on, but the brake pedal not depressed) a few LEDs in the high level brake light illminate dimly, if i replace the LED bulbs with the filament ones the LED remains extinguished in tail light only.



Does anyone know why this is happening? I assume its something to do with the LED bulbs having lower resistance than the filament counterparts so some voltage is 'leaking' through to them? Can i put a resistor in the line of the power to the high level brake light to solve this? If so what value of resistor would you suggest?



Thanks for any and all help



Matt


Don't know if this assists, but here is the circuit for the stop lights on my car, i have the high mounted stop lamp installed in the rear spoiler

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Thanks

Matt

Don't know if this assists, but here is the circuit for the stop lights on my car, i have the high mounted stop lamp installed in the rear spoiler, and the the diagram for the tail lights

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Thanks

Matt

If you purchased LED replacements for your cars tail/break lights they should work just by installing them. No resistors or magic wands should be necessary. When you say some LEDs are dim, isn't that the way they are supposed to be in the non-breaking condition?

Tom

Where are you picking up the +12 for the third brake light? You might need an isolation diode - can you draw a simple ASCII diagram of how things are hooked up now?

And, FWIW, the "tail" and "stop" light arrangement is pretty much the same as we do it in the US, and probably most cars around the world; they might use different words in different countries, but the effect is the same.

Sometimes the "tail" lights are called "running lights" which would be in parallel with the "parking lights".

What this leads up to is that there could be a miswire someplace, but to really understand the situation I'd need a diagram or something. (I think I'm half right-brained. ;-) )

Good Luck! Rich

Rich

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