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Brake lights

873 Views 5 Replies 6 Participants Last post by  John_Muha
I have '67 malibu when the headlights are off the brake lights work.At night when I turn the headlights on the taillights come on and stay on but when I press the brake the brake lights never come on. I haven't had a chance to dig into it yet I was just wondering if anyone might have seen anything like this before and might steer me in the right direction.
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Dean:
maybe the "tail" and "brake" wires are reversed and when the headlights are on, the brake lights are also on
The brake lights (now tail light filaments) would not show because they are dimmer
Give you something to think about. It's an open ground like Old Longboarder mentioned.
Think about the circuit this way. Assume an open ground to only one of the rear sockets.
Light bulbs are only resistors. They are basically Tungsten and have a very low resistance value if you measure them with an ohmmeter. The 1157 lamp has two filaments that are tied together at the base (ground). You have 2 series resistors that are different values. If the base is not tied to ground you only have 2 connections to the lamp.
If you apply 12 volts to the brake filament, without the ground to the lamp, it can light. It finds ground through taillight (running) filament "resistor", through the other rear tail light lamp "resistor" (brown wire goes to both lamps), and then to ground.
This work fine until you apply 12 volts to the tail lights (brown) by pulling on the head lights. Now the brake filament can't light because you have near 12 volts on each side of it. 12 volts applied to yellow/green and 12 volts applied to brown.
Have a safe trip.
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