Editing How do turn signals work? (section)
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==Power feed and flasher unit== 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 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. 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. 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 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 more current draw through the flasher unit, the faster it opens and closes the contact. The typical causes of this type of failure are: *Exceeding the lamp count. *Exceeding the recommended wattage of the bulbs. *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). *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. 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. 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.
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