How do turn signals work?
From Crankshaft Coalition Wiki
(http://mahohmie.qsh.eu/resource1898.htm) |
(→Power feed and flasher unit) |
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==Overview== | ==Overview== | ||
| + | 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. The following procedures will cover most of the basic and common problems found in the turn signal system. | ||
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| + | ==Problems== | ||
| + | Most commonly, problems occur when the system is wired incorrectly or bulbs are inserted into worn sockets upside down. This can cause malfunctioning of the brake lamp system, turn signals, 4-way emergency flashers, and brake lights (among other things). | ||
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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 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." That's typically where the trouble begins. | 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. | ||
| + | The turn signal shares the ground with the park light in the front of the vehicle. If the ground is loose or not connected, it can allow voltage to back feed from the park lights to the turn indicator. | ||
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| + | If you have LED lights on the vehicle, you often will need 1K ohm pull-down resistors on left and right turn to | ||
| + | bleed off residual voltage. Check with a digital volt meter, look for 3 volts or more still sitting on the turn | ||
| + | signal wire. Another possibility is if they don’t have a good ground, the PARK and TURN bulb filaments | ||
| + | are both tied together and go to body ground like a “Y”. If this ground wire is not connected, the park | ||
| + | light can back-feed to the turn signal circuit. If you use LED lights for your turns/brakes, you | ||
| + | either need load balancers to draw enough current for the flasher to work or you should use | ||
| + | a No Load Flasher. | ||
| − | ==Power feed and | + | ==Power feed and flasher unit== |
| − | Power on a traditional | + | Power on a traditional turn signal flasher unit is delivered to the system via the flasher unit. A fused, switched lead is run from the fuse buss to the flasher, so that it only receives power in the "Hot in Run" position. |
| − | From the flasher, a wire is run to the center wiper (or | + | From the flasher, a wire is run to the center wiper (or movable 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 (or "power output" side) of the contact. The bi-metallic strip functions as it does by two dissimilar metals (Bi-metallic) with dissimilar expansion rates causing it to bend. | 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 bi-metallic strip functions as it does by two dissimilar metals (Bi-metallic) with dissimilar expansion rates causing it to bend. | ||
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This occurs because the lamp load on the bimetallic strip inside the flasher unit has been reduced to a point where the time allotted for heat is extended (slowing the flash rate), or never reaches the heat point of the strip (turning on and staying on). | This occurs because the lamp load on the bimetallic strip inside the flasher unit has been reduced to a point where the time allotted for heat is extended (slowing the flash rate), or never reaches the heat point of the strip (turning on and staying on). | ||
| − | When these flash units fail, it's usually because the load on the strip has exceeded its capability to recover, and the strip just melts, leaving the switch contact side " | + | When these flash units fail, it's usually because the load on the strip has exceeded its capability to recover, and the strip just melts or distorts, leaving the switch contact side "open” from power. This is when we normally put in a new flasher. Causes of this type of failure can include age of the flash unit, overtaxing of the lamp load (as in trailer lamps), or a short within the electrical system. |
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. | ||
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*Exceeding the lamp count. | *Exceeding the lamp count. | ||
*Exceeding the recommended wattage of the bulbs. | *Exceeding the recommended wattage of the bulbs. | ||
| − | *Installing the wrong bulb in the system ( | + | *Installing the wrong bulb in the system (i.e.: a single element bulb, instead of a dual). |
*Shorting of the lamp system (common culprit: trailer plugs). | *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. | *The addition of extra lamps (such as a trailer) in the circuit, without upgrading the flash unit. | ||
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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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| + | CORRECT FLASHER CONNECTIONS: | ||
| + | The flasher normally will have two terminals: X = incoming power L = Load / lights | ||
| + | No-load flashers will have a 3rd connection for ground. | ||
| + | If X & L are swapped, the flasher wont operate properly when LED lights are installed but regular bulbs would not be affected and would seem to work normal. | ||
==The turn signal switch== | ==The turn signal switch== | ||
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This switch is wired traditionally as such: | This switch is wired traditionally as such: | ||
| − | *The center wiper ( | + | *The center wiper (movable contact or cam contact) is lamp output. |
*The normally closed contact is brake lamp power from the [[brake lamp switch]]. | *The normally closed contact is brake lamp power from the [[brake lamp switch]]. | ||
*The normally open contact is power from the flash unit. | *The normally open contact is power from the flash unit. | ||
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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). | 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). | ||
| − | == | + | ==Function== |
In review, the system works in the following manner. | In review, the system works in the following manner. | ||
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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. | 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== | ==Turn signal system troubleshooting== | ||
===Single lamp failures=== | ===Single lamp failures=== | ||
| + | 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. | ||
| − | + | ====How to check for power at the socket:==== | |
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#Get your DVOM out, set it for volts scale, V X 50 or higher, and turn the key on then the offending signal. | #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. | #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. | ||
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===Dead system=== | ===Dead system=== | ||
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If none of the turn signal functions work at all, follow the steps below. | If none of the turn signal functions work at all, follow the steps below. | ||
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#If it reads infinite, it is open. Replace the fuse and test the signal system again. If it reads 000, it is good, put it back in the buss box. | #If it reads infinite, it is open. Replace the fuse and test the signal system again. If it reads 000, it is good, put it back in the buss box. | ||
#Next, set your meter to DCV, V X 50 or auto range, turn the key on, and remove the flasher. Place the black probe on ground, the the other into either of the two flasher terminals. One will read infinite, the other should read 12 volts. If you have that, power is good to the flash unit. | #Next, set your meter to DCV, V X 50 or auto range, turn the key on, and remove the flasher. Place the black probe on ground, the the other into either of the two flasher terminals. One will read infinite, the other should read 12 volts. If you have that, power is good to the flash unit. | ||
| − | #Next, set your meter to ohms, RX1 scale and measure across | + | #Next, set your meter to ohms, RX1 scale and measure across the pins or wires. Repair or replace as required. |
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#If you don't have either a cut condition, or a burned socket, and still dead, check any lead front, or rear of the selected side. It should have 12 volts, either steady or intermittent on it. If not, your trouble is in the column harness between the plug and the switch. Or, the switch itself is bad. Repair or replace as required. | #If you don't have either a cut condition, or a burned socket, and still dead, check any lead front, or rear of the selected side. It should have 12 volts, either steady or intermittent on it. If not, your trouble is in the column harness between the plug and the switch. Or, the switch itself is bad. Repair or replace as required. | ||
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===Front signals work, but rear signals are dead (or vice-versa)=== | ===Front signals work, but rear signals are dead (or vice-versa)=== | ||
| − | #Isolate the two wires on the effected end from the column plug. Using your voltmeter, set to the above parameters, select a side, and measure the wire from the plug. It should show 12 volts (solid or intermittent). If | + | #Isolate the two wires on the effected end from the column plug. Using your voltmeter, set to the above parameters, select a side, and measure the wire from the plug. It should show 12 volts (solid or intermittent). If the socket ground and a known good ground. If it shows 12 volts, you may have an open ground wire. Replace or install a ground from each socket to a hard frame ground, following proper bonding procedures (star washers and burnishing). |
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| − | + | ===Left or right side turn signals dead=== | |
| − | + | Follow the same procedure as outlined for front or rear dead above. However, apply it to the affected side. | |
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===All rear turn signals flashing=== | ===All rear turn signals flashing=== | ||
Inspect the turn signal switch for a short between the brake lamp circuit and the signal circuit. Check the column plug and harness for shorts. Ohm the harness out with no power on, but either side selected. You should have no reading from the selected side to the brake lamp circuit, and continuity in the "Off" position to the brake lamps. If not, inspect the switch and harness, and repair or replace as needed. | Inspect the turn signal switch for a short between the brake lamp circuit and the signal circuit. Check the column plug and harness for shorts. Ohm the harness out with no power on, but either side selected. You should have no reading from the selected side to the brake lamp circuit, and continuity in the "Off" position to the brake lamps. If not, inspect the switch and harness, and repair or replace as needed. | ||
| − | == | + | ==Tools, materials, and equipment== |
| − | + | *Digital Volt-Ohm Meter | |
| − | + | *Jumper wire set | |
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| − | * | + | |
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*An accurate diagram | *An accurate diagram | ||
*Contact cleaner | *Contact cleaner | ||
*Acid brush | *Acid brush | ||
| − | * | + | *Standard hand tools |
*Dental pick | *Dental pick | ||
*Emery cloth | *Emery cloth | ||
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[[Category:Electrical]] | [[Category:Electrical]] | ||
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