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I had a little bit of trouble understanding what you wrote…
You swapped sides, but you also said the problem is intermittent so did you give the bulb enough time to act up?
Are these LEDs stock or aftermarket…if they are aftermarket switch to stock and see what happens. You say it’s a 2010 so there’s a good chance the lighting is computer controlled and sometimes aftermarket stuff causes a computer to not like what it sees on the circuit and shut down the circuit (or do something else weird).
I assume you haven’t been blowing fuses so it’s probably not a short to ground. Look for a loose connection (like in the wiring harness) or a loose/bad ground. However if your lighting is computer controlled like I mentioned you won’t actually blow a fuse the fuse may be internal to the computer so in that case you could have a short to ground.
[quote=”Tony214447″ post=138465]i did leave it on long enough to act up but why would it only do it to the one side[/quote]
The reason it did it on only one side is because of the differences between light bulbs and LEDs.Standard bulbs have an incandescent filament. In electronics terms, this is pretty much just a resistor. The LED on the other hand is not a resistor, it is a diode. Without getting overly technical about the differences between resistors and diodes, let’s just say that to the truck’s electrical system, the LED ‘looks’ like a dead short in one direction of current flow (no resistance) and an open circuit in the opposite direction (infinite resistance). The standard bulb’s resistive filament is neither a short nor an open and allows a small amount of current to flow in both directions. That is why LEDs have polarity (a + and – terminal) and standard bulbs do not. What you experienced is a normal occurrence based on how your truck’s electrical system is designed and is NOT a fault in the system.
[quote=”cap269″ post=138477][quote=”Tony214447″ post=138465]i did leave it on long enough to act up but why would it only do it to the one side[/quote]
The reason it did it on only one side is because of the differences between light bulbs and LEDs.Standard bulbs have an incandescent filament. In electronics terms, this is pretty much just a resistor. The LED on the other hand is not a resistor, it is a diode. Without getting overly technical about the differences between resistors and diodes, let’s just say that to the truck’s electrical system, the LED ‘looks’ like a dead short in one direction of current flow (no resistance) and an open circuit in the opposite direction (infinite resistance). The standard bulb’s resistive filament is neither a short nor an open and allows a small amount of current to flow in both directions. That is why LEDs have polarity (a + and – terminal) and standard bulbs do not. What you experienced is a normal occurrence based on how your truck’s electrical system is designed and is NOT a fault in the system.[/quote]
You’re totally right about there being differences between LED’s and Incandescent. It would be interesting to know what the computer doesn’t like about LED’s. An LED’s is actually not a dead short. All diodes drop voltage…a very powerful led can drop 3V or more so with a 14.5V system they would be wired in series with an additional resistor to drop the remaining voltage (i.e. the current is limited). The best guess I have as to why the computer is shutting down the circuit is that there may be a bias voltage on the circuit that the computer is using to monitor the circuit and the LED is not responding to the bias like a filament would. Or the computer is seeing that the circuit is not pulling the correct amount of current because LED’s are more efficient than filaments. You make a good point about the polarity and you’re absolutely right. That could be the real cause because it’s occurring only on one side. With a regular bulb it doesn’t matter how it’s installed but maybe the socket on that one side is causing the LED to be installed in reverse. Or maybe the OP just happens to always install it that way on that side for whatever reason.
I didn’t really want to turn this into a technical discussion about electronics. I also didn’t say an LED ‘was’ a dead short, I said that it ‘looked’ like one to the electrical system because it has nearly 100% current conductance when forward biased. It has nothing to do with the 0.7v PN junction forward voltage drop. A diode is basically just a PN junction device. In other words, If you imagine a PN junction like being a door, and apply 12.0v to this diode, it will need 0.7v of the 12v to ‘hold the door open’ and the remaining 11.3v will pass through the junction to the other side. The diode turns off when the applied voltage falls below 0.7v. A diode will not conduct in either direction if the circuit voltage it is less than 0.7v. LEDs do not drop voltage. They consume power (using a portion of the electricity to produce light), which is function of voltage times current. That is why they have a voltage rating and must have a current limiting resistor. The voltage across the resistor becomes supply voltage minus LED operating voltage. So, if you have a 12v system running a 2v LED, you will see 10v dropped across the resistor. That follows Ohm’s Law. Without the resistor, the LED will not last very long once the voltage exceeds its forward operating voltage, because it will try to consume ALL of the voltage to convert to light, and fry. This behavior is due to Kirchoff’s Voltage Law.
As for computer control, that isn’t an issue in this case. On most vehicles, any controlled lights are simply ground side switched by the computer turning a transistor on and off. Anyway, the reason this issue occurred is that one LED (diode) became forward biased (when voltage across the diode in the correct polarity exceeded 0.7v) and began to conduct current (not voltage) causing the LED to glow while the other LED was reverse biased (or non-biased) and so appeared as an open circuit which is why it didn’t glow. This is probably because LEDs do not like like being connected in parallel, which is most likely how this brake light circuit was designed. Another issue is when LEDs are put in flasher circuits such as turn signals. The LEDs draw is so little that the bimetal strip in the flasher never heats up enough to break the circuit so the LED remains on and doesn’t flash OR the LED appears as an open so the circuit flashes rapidly like when a bulb burns out. The bottom line is, before changing standard bulbs out for LEDs, the circuit itself must be able to accommodate the differences between standard bulbs and LEDs.
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