How do turn signals work?
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| − | Turn signals are one of the most misunderstood sub-systems in | + | Turn signals are one of the most misunderstood sub-systems in vehicles today. They really are simple when you stop and think about how the system performs its job, and why it is wired the way it is. Most commonly, the system is mis-wired and interacts with the brake lamp system causing non functioning turn signals under braking conditions, and 4-way flashing action when not in braking mode. |
==Overview== | ==Overview== | ||
| − | The turn signal system | + | The turn signal system is isolated from other lamp circuits, but appears to function with the brake lamp system, which, in part, is true. |
| − | The turn signal on a traditional system is a shared element with the brake lamp function at the bulb to the rear of the vehicle. The most common misconception is "I can wire my turn signals and brake lamps together at the light housing and it will be fine" | + | The turn signal on a traditional system is a shared element with the brake lamp function at the bulb to the rear of the vehicle. The most common misconception is "I can wire my turn signals and brake lamps together at the light housing and it will be fine." That's typically where the trouble begins. |
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From the flasher, a wire is run to the center wiper (or moveable contact) of the turn signal switch inside the steering column. | From the flasher, a wire is run to the center wiper (or moveable contact) of the turn signal switch inside the steering column. | ||
| − | The flasher operates from internal heat on a tungsten bi-metallic "strip" that makes or breaks the contact at the switch side | + | The flasher operates from internal heat on a tungsten bi-metallic "strip" that makes or breaks the contact at the switch side (or "power output" side) of the contact. |
| − | As the system lamp load is imposed on the flasher unit, the bimetallic strip heats up, and curls up, breaking contact to the switch. It then cools down very rapidly, and makes contact again, the lamp load again heats the strip and it opens up. Thus: flash. | + | As the system lamp load is imposed on the flasher unit, the bimetallic strip heats up, and curls up, breaking contact to the switch. It then cools down very rapidly, and makes contact again, and the lamp load again heats the strip and it opens up. Thus: flash. |
When the load is under-matched to the flash unit (bulb(s) burned out), the flash cycle is slowed or stuck "On”. This is what we perceive as a lamp outage. When this occurs, we pull over and have a new bulb put in. | When the load is under-matched to the flash unit (bulb(s) burned out), the flash cycle is slowed or stuck "On”. This is what we perceive as a lamp outage. When this occurs, we pull over and have a new bulb put in. | ||
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The other side of the coin is too many bulbs within the lamp load circuit, which taxes the flasher unit. This causes the bimetallic tungsten strip to heat and cool at a very rapid rate. | The other side of the coin is too many bulbs within the lamp load circuit, which taxes the flasher unit. This causes the bimetallic tungsten strip to heat and cool at a very rapid rate. | ||
| − | The more current draw | + | The more current draw through the flasher unit, the faster it opens and closes the contact. |
| − | The typical causes of this type of failure are | + | The typical causes of this type of failure are: |
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| + | *Exceeding the lamp count. | ||
| + | *Exceeding the recommended wattage of the bulbs. | ||
| + | *Installing the wrong bulb in the system (ie: a single element bulb, instead of a dual). | ||
| + | *Shorting of the lamp system (common culprit: trailer plugs). | ||
| + | *The addition of extra lamps (such as a trailer) in the circuit, without upgrading the flash unit. | ||
To prevent this malady from occurring, always install the recommended wattage or bulb number when replacing the bulbs. | To prevent this malady from occurring, always install the recommended wattage or bulb number when replacing the bulbs. | ||
The net result usually is a very rapid flash rate. And in some cases, failure of the flasher unit, or premature failures on subsequent units. | The net result usually is a very rapid flash rate. And in some cases, failure of the flasher unit, or premature failures on subsequent units. | ||
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==The turn signal switch== | ==The turn signal switch== | ||
| − | This little switch has been responsible for more "hair pulling” incidents than most other parts of the vehicle. When you understand how | + | This little switch has been responsible for more "hair pulling” incidents than most other parts of the vehicle. When you understand how it works, and why it works the way it does, it’s really quite simple. |
At the bottom of the steering column on traditional turn signal systems, there is a plug. From that plug all the system signals (power) go in and come out. And, an added system, a wire from the brake lamp switch. | At the bottom of the steering column on traditional turn signal systems, there is a plug. From that plug all the system signals (power) go in and come out. And, an added system, a wire from the brake lamp switch. | ||
| − | At this plug you will find flash unit power in to the switch handle, two sets of wires for the left and right turn signal lamp socket power | + | At this plug you will find flash unit power in to the switch handle, and two sets of wires for the left and right turn signal lamp socket power (front left, rear left, front right, and rear right). These wires bring power to the lamps for turn signal AND brake lamps to the rear. Also at that plug you will find a wire for the brake lamp system from the brake lamp switch. |
| − | The switch itself, | + | The switch itself, located below the horn ring on most traditional systems, is like any other, except that it is two switches in one, the left side and the right side. It also provides the isolation required between the brake lamp system and the turn signal system. |
| − | To understand how the switch works, we can view one side of it for an example. If you remove the | + | To understand how the switch works, we can view one side of it for an example. If you remove the steering wheel, (and usually the horn assembly) you can see the turn signal switches. They are usually on a plastic base plate, driven by a plastic cam, and set off by two "spring steel" contacts that shift contact points when the base plate is activated with the turn signal arm. |
| − | Let's look at the left side only for now | + | Let's look at the left side only for now. |
| − | As you activate the left turn signal, the | + | As you activate the left turn signal, the cam rotates, and the spring steel contact flexes, removing contact from the normally closed contact to the normally open contact. |
This switch is wired traditionally as such: | This switch is wired traditionally as such: | ||
| − | The | + | *The center wiper (moveable contact or cam contact) is lamp output. |
| − | The | + | *The normally closed contact is brake lamp power from the brake lamp switch. |
| − | The | + | *The normally open contact is power from the flash unit. |
| − | When | + | |
| + | When no activation is present at the turn signal, the brake lamps are configured to light when the pedal is depressed through the normally closed contact of the switch and the center wiper (lamp output). | ||
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| + | Now, assuming you are at a stop light, turning left, here's what happens: | ||
| − | + | The contact switches power when activated by the cam assembly, and opens (or turns off) the left brake lamp from the normally closed contact. And, it now has contact between the center wiper (lamp output) and the normally open contact (the flash unit). | |
| − | + | If the brake lamp and the turn signal were both on at the same time, you would never see the flashing of the signal. Since the same filament is shared by both systems, even though both would be operable, when the flash unit was off, the brake power would still be on, making no noticeable change in the bulb. | |
If it were wired this way and both brake lamps were common to each other on the power leg. AND no brake pedal was pushed (brake power off) BOTH rear lamps would flash together. | If it were wired this way and both brake lamps were common to each other on the power leg. AND no brake pedal was pushed (brake power off) BOTH rear lamps would flash together. | ||
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