Brake Lights versus Turn Signal 1

[7carisfast]

Do any of you know the common way of how turn signals (pulsed signal) cancel the brake lights (steady when brake is depressed) in automobile applications?

 

[itsmoked]

Off hand I don't remember but I suspect it's related to the bazillion wires running up to the turn signal switch - way out of rational proportion. So the break light signal could be disconnected and the flashing signal connected in one motion of the turn signal switch.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MikeHalloran]

That's how it works in older cars.

Now, mostly, they just keep the circuits, and the lamps, separate.

I guess the cost of a CAN bus node with drivers has not yet come down far enough to simplify the wiring more. I had expected it to amount to one fat wire and one skinny wire to each corner of the car by now.



Mike Halloran
Pembroke Pines, FL, USA

 

[ScottyUK]

Don't US cars simultaneously illuminate brake and turn signals? UK cars do: you can often tell if you are following a Ford older than three years, even in total darkness and from a distance, because the turn indicator modulates the brake light.


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If we learn from our mistakes I'm getting a great education!

 

[BrianG]

Scotty, I am UK based and would disagree with your statement about UK cars all doing this. Those that do are usually because of a poor earth connection to the rear light unit. It's an MOT failure if they do!

 

[ScottyUK]

Disagree with what - brake and turn indicator can be simultaneously illuminated, or brake and turn lights interacting?

The first statement is definitely true: the brake lights illuminate when the brake pedal is pressed while the turn indicator is also operating. The functions are independent: operation of one does not prevent the other, nor should it cause the other to operate Go try it if you don't believe me!

I agree that there should not be a case where braking causes the turn indicator to illuminate, nor where the turn indicator causes the brake light to illuminate. This interaction is a common problem with older Fords for exactly the reason you give: bad earthing. I've repaired so many for friends and family over the years that I have lost count. I think all were Fords except for my Renault Laguna. I don't think I said all UK cars suffered from the problem, just that when it does happen it is very often a Ford which is affected.

Have we dragged this thread sufficiently off topic yet?


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If we learn from our mistakes I'm getting a great education!

 

[bogeyman]

In my old austin healy 100 (1954 when flashing turn indicators were a novelty on the UK roads) there was a dual relay box (one relay for each side) which took both the brake lamp and signal wires in and sorted out which feed to send to each lamp, it was a standard Lucas part. If I can find the service book I may be able to get a wiring scheme to you.

 

[7carisfast]

Guys, I think I figured it out while not sleeping over this question. Your turn signals have two independent relays, one for the left, one for the right. When you activate the turn signal, it energizes a relay. The relay has a maintained contact which opens up the brake circuit if energized and the second contact is an pulsing contact which pulses the turn signal light.

 

[waross]

In the older North American cars there is no relay. There are brake lights. The turn signal switch would interrupt the connection to one brake light and connect the flasher in the circuit. Newer cars have separate brake lights and turn signal lights. Red for brake/stop, amber for turn.

Bill
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"Why not the best?"
Jimmy Carter

 

[VEBill]

A related point:

In Canada (and elsewhere), all cars are now equipped with Daytime Running Lights (DRL).

Some poorly-designed cars combine the DRLs with the front turn signals. The net result is that you often see a car coming towards you with one light on and one light off. For just about a second you have no idea if they'll be turning left, or right, or if they simply have a burned out bulb. You have to wait for a second or so to see if and which light actually completes the off-on blink cycle to figure out their intentions.

Anyway, this circuit would be virtually the same function as the old Ford (and others) combined brake lights and rear turn signals.

 

[cb92]

I definately agree with itsmoked that the turn signal switch must break the circuit to the brake lite and then send power to one element thru the flasher (keep in mind that there was only one flasher on the cars we're talking about). It always marveled me how one switch could make a circuit and break a circuit at the same time, one of the things that started my interest in engineering.

 

[itsmoked]

And so goes the deep societal impact of the lowly turn-signal.

Keith Cress
kcress -

http://www.flaminsystems.com