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We don't know what the reverse trigger circuit looks like, so we don't know what effect it could have on an open circuit. It can't be purely grounded at the head unit end because something has to be there to sense voltage. That something could easily induce a small leakage current that would raise the voltage in the circuit.

For the record, infinite resistance is greater than any resistance, so an LED does indeed have a higher resistance than an incandescent bulb. Regardless, since some current does flow through the LED as long as it is emitting light there has to be some value of resistance that can be calculated using V=I*R.
 

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Discussion Starter · #182 ·
rockinpirate,

Did you try working/testing everything without a backup light bulb of any kind installed? Test the system with the backup socket empty and see what happens. Maybe something will be learned.
 

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2007 Saturn Sky Redline. 5-speed, gray. 87k miles on body. 1k miles on crate engine and turbos.
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No, not yet. But I can. It's a driver, not a garage dwelling investment. lol Biggest problem is finding a seller that you can talk to, that really knows LEDs. It's frustrating, and I really appreciate you guys hanging in there with me. More than you know.

I knocked out the other LEDs in nothing flat. Didn't even have to take the mirror off to install them. It was sweet tonight as we drove it to a ballgame. Huge difference!

In my feeble mind, it has to be not enough resistance or something like that. Almost every seller says it may need a resistor to work right, even the auto parts stores.... But I don't want to start cutting wires just to find out. The bulbs jump out on their own now, almost. Ha
 

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Trying without a bulb is a good idea, and should tell us quite a bit about what the problem is.
 

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Well tomorrow is here, and the incandescent bulb is out........ There is no bulb in the socket at all... And the radio is acting the same way as it did when the LED was installed. "No Video Signal" is all that is displayed on the screen, unless the car is in reverse. Then the rear camera works perfectly.

(I went to sleep thinking about this, and woke up at surnrise thinking about it. lol Couldn't wait to get an answer to the remove-the-bulb test).
 

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Infinite resistance is an open circuit - zero electrons can pass. Definitely high resistance! But not in the way you intended, I think. Zero resistance on the other hand is a short circuit. Diodes have both, depending on direction. An "LED bulb" though definitely has some resistance because...there are resistors on board! (for current limiting aka ballast)

Anyway, my recommendation to rockinpirate is still to try a 3157 with CANBUS compatibility. Again, CANBUS bulbs do not communicate on the CANBUS...they just "do no harm". Part of that is through increased resistance - they make the circuit believe a bulb is installed and working. Heck, if I lived in the same country, I’d send him one since I have a spare! But really, these are pretty simple to find...lots on Amazon and likely available at the local auto-parts store as well. Should clearly show "CANBUS" on the label somewhere. As I've said, just far easier to try first than tapping in a resistor.
 

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I'm trying to find one locally. Most auto parts stores don't know what I'm talking about when I say CANBUS. Probably have to buy one online. Thanks!

Surfing online.. They are still hard to find. CANbus with no load resistor needed are easy to find in colors, like for turn signals. Hard to find in white for reverse light. Can get pricey, too. I wouldn't mind paying $40+ if I was sure it would work.
 

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I'm going to give these a try. Good reviews. Have their own website (not just eBay or Amazon seller).
Says "error free" and "CAN-BUS".

 

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I'm going to give these a try. Good reviews. Have their own website (not just eBay or Amazon seller).
Says "error free" and "CAN-BUS".

Those may have a low enough resistance to solve your problem. We'll hope for the best!
 

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Thanks, John. We'll find out Friday. If that doesn't fix the problem, I'll find the brightest halogen bulb I can find, and move on. Spent enough time on this project

Enjoying my LED interior LEDs. I kinda chuckled when I put thesp lights in. Lot less trouble than Mike's House of Mods had. Didn't even take the mirror off. Just used a tiny flathead screwdriver and a c-clip expander. EZPZ.
 

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Infinite resistance is an open circuit - zero electrons can pass. Definitely high resistance! But not in the way you intended, I think. Zero resistance on the other hand is a short circuit. Diodes have both, depending on direction. An "LED bulb" though definitely has some resistance because...there are resistors on board! (for current limiting aka ballast)

Anyway, my recommendation to rockinpirate is still to try a 3157 with CANBUS compatibility. Again, CANBUS bulbs do not communicate on the CANBUS...they just "do no harm". Part of that is through increased resistance - they make the circuit believe a bulb is installed and working. Heck, if I lived in the same country, I’d send him one since I have a spare! But really, these are pretty simple to find...lots on Amazon and likely available at the local auto-parts store as well. Should clearly show "CANBUS" on the label somewhere. As I've said, just far easier to try first than tapping in a resistor.
An LED does not really have zero resistance in one direction. The forward voltage drop of a discrete LED varies, but a reasonable range is from 1.2 to 4 V, with an allowable current in the range of 30 to 100 mA. The ballast resistor is wired in series with the LED to limit the current to the acceptable value for the LED used, since powering a single LED with 14.2 V will almost certainly exceed the allowable current and destroy the LED. The value of the resistor needed depends on the number, specification, and arrangement of the LEDs used, with (for example) 12 LEDs with a 1.2 V forward voltage wired in series actually requiring no resistor at all, since 12 times 1.2 V equals the 14.4 V of an automotive circuit.

CANBUS LEDs, from what I have been able to learn, add a resistor in parallel to the primary LED circuit i order to increase the current through the lamp assembly. This gives the lamp enough current for the sensing circuit to reliably detect it, where the normal LED current does not. So CANBUS LEDs actually have a lower resistance than a "normal" LED, but a higher resistance than an incandescent bulb.

While it is not the case with the Kappas, since they were designed to operate with incandescent bulbs, a CANBUS LED can "do harm" to a circuit that is designed for standard LEDs because the current that they draw is higher due to their lower resistance.
 

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CANBUS LEDs, from what I have been able to learn, add a resistor in parallel to the primary LED circuit i order to increase the current through the lamp assembly. This gives the lamp enough current for the sensing circuit to reliably detect it, where the normal LED current does not. So CANBUS LEDs actually have a lower resistance than a "normal" LED, but a higher resistance than an incandescent bulb.

While it is not the case with the Kappas, since they were designed to operate with incandescent bulbs, a CANBUS LED can "do harm" to a circuit that is designed for standard LEDs because the current that they draw is higher due to their lower resistance.
My understanding (and agreement) too.
 

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And As the Kappa World Turns.... We await the arrival of these....
Light Product Automotive tire Font Line


You guys are amazing. I can tell the time, but I have no idea how the watch is made.
 

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I agree with much of this. I did review my posts and catch myself saying "adding resistance", which is technically very not correct. I should have said "adding load", which is done here by adding a resistor. "Adding a resistor" though definitely does not equal "adding resistance" to the circuit so my bad.

Just careful when you intermix "current" with "voltage". LEDs have a forward voltage drop, so the supply voltage must be higher than the drop for current to pass. Powering a single LED with 14.2V is exactly what happens! Resistors don't change voltage - they limit current. So it's not the voltage that will kill the bulb if no resistor is present - it's the current.

Edit: I take that back..."adding resistance" IS actually the correct term.
 

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Discussion Starter · #196 ·
Two or three years ago, I bought a high intensity fancy looking LED bulb for my backup light that may be the exact one you pictured. I had a problem with it snapping into the socket like the original incandescent bulb did. It went all the way in, but had no retention. I ended up wedging the end of a toothpick into the socket latch to clamp it hard to the base of the bulb which worked perfectly. So if you find that to be a problem, try the toothpick trick.
 

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I agree with much of this. I did review my posts and catch myself saying "adding resistance", which is technically very not correct. I should have said "adding load", which is done here by adding a resistor. "Adding a resistor" though definitely does not equal "adding resistance" to the circuit so my bad.

Just careful when you intermix "current" with "voltage". LEDs have a forward voltage drop, so the supply voltage must be higher than the drop for current to pass. Powering a single LED with 14.2V is exactly what happens! Resistors don't change voltage - they limit current. So it's not the voltage that will kill the bulb if no resistor is present - it's the current.

Edit: I take that back..."adding resistance" IS actually the correct term.
Actually you were closer to correct the first time. The CANBUS LED lamps add a resistor, but because it is wired in parallel to the standard lamp's LED and ballast resistor, it decreases the resistance of the lamp. This increases the current through the lamp, thus increasing the load on the circuit.

You may be powering an LED lamp with 14.2 V, but that lamp is comprised of (at least) one discrete LED and one resistor, and the LED (or each LED if there is more than one) is only going to see its rated forward voltage and rated current.

Current and voltage are inextricably related in a circuit, especially so for a resistive one. You cannot have current without voltage and, unless it is an open circuit, any time you have voltage you will have a proportional current. You can split hairs about what causes the damage, but since the current that causes the damage is created by the voltage across the LED, it is fair to say that it was too much voltage that caused the failure. Keep in mind that the vehicle's electrical system is a voltage source and not a current source since it is the system's voltage that is regulated.

Also, resistors do change voltage in any circuit that has current flow, because there is a current-induced voltage drop across the resistor. Put two resistors of equal value in series across a 12 V power supply, then measure the voltage at the junction of the two resistors. You will see that it is 6 V, so the resistor has changed the voltage at that point in the circuit.

Assume you are using an LED with a forward voltage of 3 V and a rated current of 250 mA in a 14.2 V circuit. You will need a resistor wired in series with that LED that will cause an 11.2 V drop at 250 mA, so its resistance should be 11.2 divided by 0.250, or 44.8 Ohms. The closest standard value to 44.8 Ohms is 47 Ohms, so that is what would normally be used.
 

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Adding a resistor in parallel will not decrease the resistance of the lamp. It will decrease the resistance of the circuit. It is a separate load, seeing identical voltage and current than the LED bulb.

And respectfully, that's the last I have to say on this subject!
 

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And respectfully, that's the last I have to say on this subject!
It’s a shame you’re done with the subject, as there’s many of us here who consider this topic a foreign language and love a bit of knowledge drop through civil discourse. Understandable though. Thanks for your thoughts on the subject while you were here...

Anyways... JohnWR, it’s my understanding that “in parallel” is the frowned upon method of wiring LED‘s because of the quadrupling of power resistor dissipation and doubling of the power dissipation of the circuit, leading to A LOT of wasted energy and additional load on the LED, reducing its lifecycle. Does any of that make sense, or am I still way off on this alien convo?

I keep my eye on a hobby (building internal chassis‘ and the electronics of lightsabers, believe it or not) and some of the wiring and lighting and batteries and spinning servos and whatnot that these wizards do makes a fella think electronics is actually all magic and voodoo!!



One day I’ll wrap my brain around it all!
 

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Adding a resistor in parallel will not decrease the resistance of the lamp. It will decrease the resistance of the circuit. It is a separate load, seeing identical voltage and current than the LED bulb.

And respectfully, that's the last I have to say on this subject!
I am using "lamp" to mean the device that you plug into the lamp socket. Since all of the components are contained within that device, adding a parallel resistor does decrease the resistance of that "lamp".
 
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