Brake light and tail light operation - help settle a bet

your right....tail lights are always on. what would happen if your brake lights burnt out.....

Generally, just look at a taillight bulb. You usually see two filaments, one is for the taillight, the second is for the brakelight. Essentially, the taillight filament is always "on" when the lights are on, and the second filament activates when the brake pedal is used.

When the lights are off, the brake pedal still activates the second filament for the brakelights.

Your buddy is wrong in saying that the tail lights go off when you hit the brakes. On most vehicles the tail and brake bulbs share the same housing and are a dual filament bulb. One side is 12-18 watts for the tail/parking lights and the other is 30-45 watts for the brake lights. If the lights are on and you step on the brake the higher wattage brake filament overpowers the other. They are both on but you cannot readily see that.

Now in some newer cars with LED bulbs in the back he is sort of correct in that they use some LEDS for double duty. They glow dim to act as parking/tail lights and when you step on the brakes they get full power and brighten up. They don't actually turn off BUT the circuitry for the lower light level is shut down.

If the tail lights shut off, then that means your light clusters have a bad ground! tell your buddy to fix his car LOL

nate

yes tail lights sty on...

Your buddy is wrong. The normal taillamp filament (parking lamp) does NOT go off when the brake lights come on.

Now, in older cars where the turn signal and brake lamp were the same physical bulb (or bulbs), the BRAKE lamp shuts off when the turn signal comes on (on one side only, obviously) so that you can see a flashing turn signal while the brakes are being used.

I've always wondered how the circuitry was wired to achieve the shutting off of the brake light (or the side light at the front) when the indicator light flashes. Seems a lot of effort compared with having a totally separate bulb and an amber filter in front of it, as they do in Europe.

When my sister lived in the US, she and my parents were hit from behind by a car that could only see the flashing indicator (the brake light on the other side was obscured by something) and who therefore didn't realise that she was stationary with the brake on rather than still moving forward. In the UK where we come from, there would have been a *separate* brake light in addition to the amber (not red) indicator to convery the two separate messages "I am turning" and "I am slowing down".

how the circuitry was wired to achieve the shutting off

The turn signal switch handles it. The brake light power runs into the switch and is sent out to the brake/turn filaments, and if you select left, let's say, the switch disconnects the left line from the brake light switch and connects it to the turn signal flasher. The right side stays connected to the brake light switch. The front turn signals are run from another set of contacts in the switch, separate from and unrelated to the brake light input. The separate turn signal light system now appearing on American cars and which has been used for years on imports works well but is a pain when connecting a trailer. An electronic adapter is required to take the two outputs (brake and turn) and convert the signal to one for the trailer bulb.

Dan

The brake light wires to each side are routed through the turn signal switch. When you signal a left turn, one set of contacts on the TS switch activates the left flasher circuit, another disconnects the brake lamp feed from the left brake/flasher bulb circuit.

At the time, amber rear turn signals were not legal in the US.

That is the sole shortcoming of the old system. Its advantage was that it removed the front/rear confusion factor. If you saw an amber blinking light, you KNEW that it was an oncoming car. Today with the mix-mash of tail lamp configurations that are allowed, amber may mean front or rear. The absolute WORST system is two separate red rear lamps ("duelling reds") where the red brake light can mask the red turn-signal light and vice-versa. I think this stupidity is only allowed in the US under current regulations. My personal preference is the old "disable the brake lamp on the turning side" but with an added center brake light to eliminate (or reduce) the confusion factor that your sister's car fell victim to.