How do turn signals work?
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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. | 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 | + | As the system lamp load is imposed on the flasher unit, the bimetallic strip heats up, and curls upwards, 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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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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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 | + | At this plug you will find flash unit power into 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 signals, 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, 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. | 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 | + | To understand how the switch works, we can view one side of it as 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. | ||
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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 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 | + | 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), then rear lamps would flash together. |
| − | In the above | + | In the above proper configuration, both systems would gain isolation from each other through the switch. |
| − | The | + | The exact same wiring is true for the right side, with one exception: the brake lamp power is picked up from the left contact (daisy chained). |
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| + | ==Functionality== | ||
| + | In review, the system works in the following manner. | ||
| − | + | When no turn signal is selected, both brake lamps will receive power when the pedal is pushed. When the left turn signal is selected, the brake lamp for the left side is disabled by the turn signal switch, and the bulb now receives power from the flash unit. At the same time, no change has been made to the right side brake lamp. The result: left lamp flashing, right lamp steady with brakes on. Right lamp is out when brakes are off. | |
| − | + | Now, switch to the right side. The reverse becomes true: the right side brake lamp is disabled, and power to the lamp is now provided by the flash unit. | |
| − | + | Brakes on or off: the left side remains on (no change to the left side) steady with brake power, and off without it. | |
| − | + | This is how the two systems are isolated. This is the most problematic issue for a novice to understand, primarily because nobody ever took the time to explain it to them in any detail. | |
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| − | + | ==Turn signal system troubleshooting== | |
| − | + | ===Single lamp failures=== | |
| − | This is | + | This is one of the most common failures found on vehicle lamp systems. The first thing to do is check the bulb. If the bulb is good, check for power at the socket. To ho that: |
| − | + | #Get your DVOM out, set it for volts scale, V X 50 or higher, and turn the key on then the offending signal. | |
| − | + | #Carefully insert the probe of your meter into the socket, to the contact pad (S) on the bottom of the socket, and the other to a good ground. | |
| − | + | #If you read 0, then 12 volts then zero (flash signal), the power to the lamps and the system are working fine. You have a bonding issue. | |
| − | + | #Shut off power to the system, and key, and return to the offending socket. | |
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| − | Get your DVOM out, set it for | + | |
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| − | If you read 0, then 12 volts then zero | + | |
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| − | Shut off power to the system, and key, and return to the offending socket. | + | |
New Cars today have Plastic Bumper’s and Anti Collision Systems. Proper Ground Bonding is becoming Scarce Compared to Bygone Days...and Lighting systems have had to relay on "Wired" or "Remote Location" Grounds. It is quite common to lose ground to a single socket and disable it. | New Cars today have Plastic Bumper’s and Anti Collision Systems. Proper Ground Bonding is becoming Scarce Compared to Bygone Days...and Lighting systems have had to relay on "Wired" or "Remote Location" Grounds. It is quite common to lose ground to a single socket and disable it. | ||
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