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Old 08-11-2012, 01:47 AM
ArtNJr ArtNJr is offline
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Originally Posted by AFMEDIC View Post
There was a recall a few years back for the wires that control the fan being too small. The wire for the power comes from the ignition. . . . It was something about the terminals heating up and expanding and not making good connection because the wires were too thin.
How many Amps a circuit can handle is determined in great part by the wire thickness (gauge, or gage) & here's a chart you can use to see what gauge should be used for a given Amp rating:

When the Amp draw is too high the circuit will overheat & not only connections, but the wire itself, which will either cause a fuse or relay to burn out or a circuit-breaker to trip, or if there isn't anything in-line to shut the circuit down, could start a fire.

And remember this simple formula: Volts x Amps = Watts (doesn't take Resistance into account, but it's close enough for most calculations). Although the Voltage in your truck will (should) be higher than 12 @ certain points you can just figure 12 for everything, so if you know the Wattage of the device being powered, you can divide that by 12 to find the Amps being used to power the device. In other words, a 60-Watt headlight would draw ~ 5 Amps, which would mean you'd need 14 gauge (or heavier) wire (the lower the gauge number the thicker the wire). The light would still come on with 16 gauge wire, but the wire & connections would get hot immediately because the light would be drawing more Amps than the wire can safely handle.

Of course thicker wire costs more & especially if you build many 1000's of a certain vehicle a small savings per vehicle translates into a lot of money, so manufacturers will use the thinnest wire they think they can get away with. And that's true for everything -- say you replace the factory stereo & speakers with ones having a much higher Wattage rating but don't change the original skinny 18 or 20 gauge wires -- the Voltage remains the same, but the Amp draw goes up & now you've got the same problem as the headlight with too light a gauge wire running to it. Crank the volume up & not only will the sound from the speakers be distorted, the wiring to & from the stereo & to the speakers will overheat, as will all the connections.

In the case of a fan which has lighter gauge wire running to it than it should, sooner or later the fan motor will burn out because it'll always run too hot. The wire itself & the connections will overheat too, so you can have several problems, all of which can be fixed by simply replacing the wire with the proper gauge. And hooking the fan motor up to a battery doesn't tell you if the motor is drawing too many Amps for the wires in the truck going to it because there's no load on the motor -- which there will be when it's installed & blowing air. But if the motor has a Watts (or Amps) rating stamped on it, you can quickly figure which wire should be used.
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