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I like the more modern look of LED lights plus the faster response time and brighter light is a safety plus.
There are a few write-ups of installing LED bulbs but these all involve adding load resistors to keep the error messages away. The problem is that most load resistors are 6-10ohm, which at 14V would be 20-30 Watts of heat to dissipate, so they are going to get HOT!
I had bought some canbus LED marker lights bulbs from CarID and these have a couple of small surface mount resistors to simulate the load of a conventional bulb. The resistance is higher than a bulb would be, so the power and heat is a lot less but it is enough to fool most systems into not throwing errors. This got me to thinking that it probably doesn't take such a big load to prevent the errors but what is the right load for our particular cars?
470ohm was a bit of a guess but it was mainly to limit the current and power dissipation in them so they wouldn't get too hot. At 14V they only need to dissipate about 0.4W. The 5mm length is important for bridging the positive and ground traces in the bulb housing. The low profile surface mount parts also means there is no interference with anything in the tail light housing so it is all completely hidden.
After some experimentation I came up with the following loads needed to keep the system happy:
Turn Signal - 120ohm
Tail Light - 120ohm (if you leave the second bulb as a conventional type)
Brake Light - 50ohm
These loads should let you use just about any LED bulb. If the bulb draws more current to operate then the controller may be happy with fewer resistors. The resistor temperatures I measured with a thermocouple were about 120F, so not very hot at all. All that metal in the traces makes a good heat sink and there is no risk of damage to any of the plastic parts.
In hindsight you could probably get by with a lower resistance and a little bit hotter operating temperature. That would reduce the number of components that needed to be soldered.
I will be the first to admit that this is an ugly solder job, in fact it may be one of the WORST I've done. But in my defense, there is a lot of thermal mass in those traces and getting them hot enough to solder to was tough. I had to use the big ole Weller solder gun which made the tiny resistors a bit of a challenge.
Close up of the tail light bulb. Kind of a neat look I think, and brighter than the regular incandescent bulb. The dim one in the center with the diffuser is the 1 remaining conventional bulb.
Conventional brake bulb on the left, LEDs on the right. When combined with Jandreu's mod to use the rear fog lights, you get double the visibility. The picture doesn't show the difference very well but the red puddle on the ground is a good indication of how much more light there is. And it is a much more vivid red.
All around I think it's a nice update to the look and maybe helps wake up other drivers a little faster.
If you want to try this I would recommend
Scuff the traces to remove any oxide. I had some trouble getting a decent solder joint before I used an emory board to clean the surface
Make sure you have something with a lot of heating power, a regular solder iron probably won't get the job done
Buy extra resistors. They are cheap, and better safe than sorry if some get damaged in the process of putting them in
Flux for the traces and solder paste instead of solder wire would probably make it easier (and your work will look much nicer than mine)
When driving at night yesterday I got a check lights message momentarily for the tail lights.
It must be a sensitivity to the voltage in the system while the battery is recharging after a start. I switched the lights off and back on again, and couldn't get the message to repeat so it must be very close to the threshold.
I added another resistor to that segment to give some more margin.
Below are the updated resistance values. I can't edit the original post any more but maybe one of the mods can change it?
Turn Signal - 120ohm
Tail Light - 100ohm (if you leave the second bulb as a conventional type)
Brake Light - 50ohm
And also when used in the dark the extra brightness blinds them, just like rear fog lights do when there is no fog and we curse the idiot in front, and then wonder why they run into the back of you when the lights go off
It's the reason Jaguar didn't fit 55w halogen stop lights
After 15 years, I have just done my 1st bling mod to my car. I installed the smoked rear lights (from the victory edition), and installed some bright Led lights as well, with the resistor setup like you (same amount as well).
They work very well, and indeed best to 1st grind away some material before you solder it.
So thanks Charlie, I really liked this neet solution for the led lights
Wow! Thanks for figuring this out. (Yes, I know it is an older thread.)
As a sorta engineer (old school software engineer when back in the day I had to design and build my own hardware) I had guessed at the problem and what would be required for the solution. Health issues, now happily resolved, prevented me from working on the solution.
Now, thanks to you, I don't have to solve the problem; I just have to implement the solution! :-)
LED Tail/Brake Bulb Installation + How-To
