Elbeau

Since all the wiring to individual bulbs is inside the headlight housing, which is virtually all plastic and smartly sealed by end caps, where can one install the LED load resistor without compromising the sealed nature of the headlight assembly? The only option I can think of is drilling a hole in the back of the headlight assembly and passing the load resistor wires through it and then seal the hole with silicone glue. But I suspect I would also have to replace, or add to, the wires on the resistor to make them long enough to get to a decent metal place to mount the resistor itself. I also considered the idea of mounting the resistor so that it is being held in the air by its wires inside the headlight housing, which would then, in theory, avoid melting plastic and also provide more air circulation to cool the resistor. But, that seems a bit iffy.

Any other ideas?

Here's the weird situation: However, on occasion, when activating the left side turn signal, the dash indicator flashes and clicks as if the left signal is hyper-flashing and I get the message that the bulb is out. However, the bulb is actually working properly and not hyper-flashing. If it's actually flashing faster than normal, it flashing fast enough to notice.

Please resist the urge to engage in discourse on the evils of LED turn signals. That's a mute issue as I already have the LEDs installed and intend to keep them.

BlownV8

Get a resistor that does not produce excessive heat. If you do, just keep it inside the housing.

Elbeau

And which would that be. They all produce heat.

BlownV8

No, there are some that will melt plastic while others produce very little heat.
No experience with this seller but these typically do not produce much heat. Ask the seller. 2x H7 Headlight LED Canbus Error Free Resistor Anti Flicker Canceller Decoder | eBay

These, they will melt your headlights/wiring if they are in the housing. Ask me how I know.
H7 LED Anti Flicker Adapter Error Free Canceler Canbus Headlight Lamps Decoder | eBay

eric_in_sd

Why are you putting load resistors on the headlights? Are you getting headlight error messages on the dash?

I took off the headlight assembly back caps when I first installed the LED bulbs. Never put them back on. They are pretty much entirely cosmetic as far as I can tell.

You don't need anything special for the load resistors. They can be ordinary aluminum shell wire-wound reistors. For the marker lights, I found that 100 ohm, 10W works fine.

Elbeau

Thanks,
I'm pretty sure I can guess about how you know.

Interestingly, I checked out the alleged God of car LEDs, Motomoro and, after they boasted about how their resistor produces half the heat of those cheapo gold colored ones and therefore are safe, they warn that the MUST be mounted with screws to metal because that tape those cheapo ones use would melt. Hmmm

Elbeau

I didn't put them on the headlights. I asking about using them on turn signal bulbs, which are in the headlight housing.

And those caps are far more than cosmetic. There are open areas inside the housing where dirt and moisture can readily get on the reflectors and wires, as well as fog the lens. Where I park are a lot of palm trees that deposit all manner of filth on the car. And, I drive in the desert and beach, so sand can and will get into huge holes at the back of the housing.

I think I found the resistors I need/want. But the issue of mounting them still remains.

Thanks for the information about the ohms & watts. That's helpful.

eric_in_sd

Power resistors - all resistors; "power" only means it is designed to run with higher than normal power dissipation - produce a certain amount of heat depending on their resistance and the voltage across them. It has nothing to do with the design of the resistor or its color. They probably want you to mount the resistor to metal so heat will be conducted away.

Elbeau

Yes, I understand that. My point is that even supposedly low heat generating resistors can get hot enough to melt plastic, as Morimoto warns about its own, after touting its supposed much lower heat generation. I think MoriMoto's reference to the gold resistors is based on so many "lesser" ones on the market being gold colored and not that the color matters for heat dissipation.

alive19

Resistors work by converting electrical energy into heat. The wattage rating of the resistor, is how much heat is produced. There is no such thing as low heat resistor, only better heat dissipation. The larger the resistor for the same wattage, the lower the temperature is likely to be, as heat energy is more efficiently dissipated.

Elbeau

Yes. Semantics. But, before that heat is dissipated, it is produced. So, my concern about how to mount the resistor is valid, despite the claims of the premium brands. Interestingly, I saw a GTR LED that pairs with a resistor apparently intended to hang in the air, suspended by its wires. The wires and connectors do look substantial though. The only substantially larger led resistor I've found is an Alla that still is supposed to be mounted to metal.

Sallad

kinda... sorta... a low Ohm resistor will create less heat than a higher Ohm resistor. As its "resisting" less current flow.

To add to the original convo... for my Audi I purchased an inline resistor that I hooked up to the LEDs. This kept the headlight factory sealed as the resistor pack was before the headlight assembly. It basically was a box with two plugs that you hooked up to the wires. Simple and cheap.

Elbeau

I'm not sure what you are saying. All the wires on the Benz enter the headlight housing through one grommet. You hooked it up in series, or? With the headlight assembly mounted it will be very difficult to determine which wires go to which bulbs outside the assembly.

eric_in_sd

For the benefit of folks learning about the subject:
The wattage rating is how much power (rate of heat generation) the resistor can handle before overheating and failing. The rating is under some standard conditions. If you put a cooling fan on a resistor, its effective power rating would go up. If you wrapped it in insulation, its power rating would go down. If you stuff the resistor inside the headlight assembly, its power rating goes down. If you place it in a well ventilated engine compartment, its power rating will go up.

To be safe, you should run the highest power rating resistor possible for a given application, within reason. Power = Voltage squared divided by resistance, P=V^2/R; in my example of a 100 Ohm 10 Watt resistor, 12V^2/100 = 144/100 = 1.44W = well within the 10W rating.

Note that adding about 1.5W to the power in the bulb circuit was enough to lift the current flow up to the point the vehicle did not think a bulb was out.

Correct; you want larger surface area because that is what is in contact with the air to conduct heat away. Many power resistors have corrugations, like tiny fins, to increase the surface area.

eric_in_sd

No, a low Ohm (low resistance) resistor will create more heat across a given voltage.

Power (the rate of heat generation) = voltage squared divided by resistance

Elbeau

So, all other things being equal, one should get a higher ohm resistor?

eric_in_sd

To properly size the resistor, figure out how much power the system needs to see flowing in order to not think the bulb is burned out. In my example, 1.5W was enough power added to the bulb to make the system happy. Thus 100 Ohms was about right. Power resistors are not generally available in that many power ratings, so pick a power rating much larger than the expected duty power - 10W was about right for my case.

A larger resistor will let less current flow and dissipate less power. That will make less heat but might not be enough current to fool the CAN bus.

sbwk

(deleting comment, already covered elsewhere)

sbwk

(deleting comment, already covered elsewhere)

Elbeau

After having the LEDs installed for about a year, with no resistors, they work great. Every once in a while, I will get a pop-up saying one of the headlight bulbs is out (usually the right, but sometimes the left). The lights, however, are actually lit. I have found that switching the light switch from Auto to Off and back to Auto solves the problem. I bought some resistors. But, since this is a once every several months thing, I haven't bothered to install them. Other than that rare warning, the LEDs work great. No flickering. No hyperflashing on the turn signals. Much better visibility and no adverse reactions from oncoming traffic.

vesiadog

OK FOR Todays lesson is the simple calculations of Wattage(power) Voltage (E) Current (I)
E/R=I …. E/I=R … ExI =W (Power) also I squared x R =P
Math examples … E/R=I…. 12volts /12 ohms =1 amp so in that case you better have a 12 watt resistor.
Metal cased resistors mounted on metal will dissipate
the heat better.
I have not looked at the described circuits you are installing the resistors in but it sounds like you are dropping voltage so the new LED bulb does not see the full 12-14 volts ??? There are also voltage limit 1 piece circuits out there that will do a better job .

Max Blast

I am continuously oppressed by everyone’s displays of math in public… but I still have the question why did the OP need to wire this in in the first place?

Sallad

The resistor?

I'm assuming he wanted to wire it in to fool the ECU.

eric_in_sd

Betty Sue desperately wanted to marry him, so she used all her feminine wiles, including making his favorite meal. He found it impossible to resistor.

Sallad

Um, what? aah, ok.