I'm a newbie to this whole LED swapping thing and I'm by no means an electrician. So far I've done the easy part (the interior and trunk) and the next step would be the exterior.

I've read that for the turn signal LED swap, load resistors are need to solve the fast blinking problem. I tried to research some more on the forum but maybe I just didn't search the right phrase. I couldn't really find how many resistors and at what rating I need, and where should I hook up the load resistors.

I've seen on eBay there're load resistors at 6 ohm/50 watt, 8 ohm/25 watt or 3 ohm with no specified wattage. They all seem to indicate I need to hook one up for each of the LED bulbs. So does that mean I need four load resistors (one for each turn signal)?

Also, are load resistors needed for the stop lights and tail lights?

If anyone that has done the exterior swap can show me the ropes I'd really appreciate it. Thanks!

 

I don't know of anyone, or heard of anyone who's done this. I don't think I'm 100% understanding what your saying either. You want your blinkers to blink faster, correct?

 

No, it's actually the exact opposite. If I swap the filament bulbs with LED bulbs, the blinker goes crazily fast. I read that I need to add load resistors to the circuit to correct the flash rate back to the normal. I'm just not sure what's rating of the load resistor I should add and how many of these load resistors do I need.

The load resistor ratings I've found on eBay include:
1) 6 ohm/50 watt
2) 8 ohm/25 watt
3) 3 ohm/?? watt

The quantity options I've found include:
a) one load resistor per side
b) one load resistor per turn signal

I can't seem to figure out which is the correct combination of the two.

And that's just for the turn signals. I have the same question for swapping filament stop light bulbs and tail light bulbs.

 

i changed my white reverse lights for leds and have the same problem. They turn off after like 2 seconds because the car thinks the bulbs are out...

 

I have replaced most of my lights with led's as of now, included are:
Park lights
interior lights(map and dome and trunk)
the full LED tail lights(look amazing)
license plate bulbs
and i also have HID's in my driving lights and fogs
also in the process of installing led strips under the seats and dash for when the doors open they will come on.

So far after replacing my tails my cruse control stopped working due to there not being any resistance in the brake lights. so the solution to this problem is to put a resistor in parallel with the brake lights. The curse stopped working( weird i know) because it senses the brake light bulb is out and it is (apparently) a hazard if you slowed down while curse is on...
Anyway the resistors you should use can be anywhere between 6ohm-100ohm... don't really matter, you just need to put some resistance on the line so the computer thinks there is something there(3 ohm might be too low). As for the wattage, the wattage rating on a resistor is the maximum wattage it can dissipate safely, so the higher the better. a 25watt, 35watt or 50watt would be fine. I am using a 6ohm 25watt resistor for my tails, haven't installed it yet, its too cold out now so I'm waiting for the summer.

 

OK I've found the answer...I swapped all four turn signals to LED, and put one 3 ohm, 50 watt load resistor on each side (one attached to front right signal and one to front left signal), and that is enough to put the flash rate back to normal. My brake lights have been swapped too and they don't seem to be affected in any way.

 

if you put the resistor in series, it should bring back the cruise. Because its in parallel, the computer is sensing across the LED instead of the LED and the resistor. Putting it in series, it will sense both and should look 'normal' to the car.

 

will you please post pictures if u have them. i have replaced my turn signals with LEDs and am having the same problem

 

I am having a problem with the cruise control after swapping out the brake lights with LEDs. What do you guys mean "putting them parallel"?

 

Ok, so I realize that this is an old thread, but that there is still confusion about Load resistors, and why we need them and where they go. I hope to clarify this for all future readers of this thread. Firstly, why do we need load resistors when installing LED turn signals. or other LED exterior lighting. Well, in short, lights use power, and some exterior lighting is monitored by the car and may be linked to certain security systems to notify the driver or to prevent unsafe operation of the vehicle. (Mostly these are break lights and turn signals) These security measures are designed around the power draw of an incandescent bulb. LEDs or Light Emitting Diodes draw very little power, in fact, they draw so little power that they can activate these security systems. For turn signals the symptoms of this would be hyper-flashing, or when your turn signal blinks really fast to tell you that one of your bulbs is out. Now we have to learn some math so we can understand where the load resistor comes in.

Basics:
Voltage[V] = Current[Amps] * Resistance[Ohms]
or Current[Amps] = Voltage[V] / Resistance[Ohms]

Power[Watts] = Voltage[V] * Current[Amps]

So, looking at the specs for a standard 7440 Incadecent bulb, we find that they are typically about 25W, so we know that at 12V they draw about 2.08A. An LED replacement for this bulb will probably draw somewhere around .115A. [Varies widely based on the type and quantity of LEDs used in the replacement 'bulb'] So, to trick the car into thinking that a regular light bulb is installed and working, you need to draw more current. LEDs themselves don't actually have resistance (they are semiconductors, which have their own unique electrical properties), so the replacement 'bulb' will have some resistor installed in the little plastic wedge part. Resistors are what 'drives' a circuit, in other words they determine the current draw. The Voltage source typically remains constant, so to change current draw you need to change the resistance. Note that in a conventional light bulb, the filament that gives off the light is actually a resistor, so that is what drives a normal lighting circuit. if you have no resistance element (or very low resistance) there is no limit to the current, and so the current will be very high (a short circuit, like putting a wrench between terminals of the battery, that arc is caused by the massive current flow because of very low resistance). Anyway, the resistor in the LED 'bulb' structure would be somewhere around 104.3Ohms in my example.

12V ~= .115A * 104.3Ohms

Now, on to the Load resistor. we need to lower the resistance, to make the current higher (to simulate the normal bulb draw of 2.08A). How do we subtract resistance you ask? good questions. Here are some equations to help.

Add Resistance in Series:
R1 + R2 = Rtotal

Parallel Resistance is more tricky:
(R1 * R2) / (R1 + R2) = Rtotal

(for pictures and wiring diagrams of how to wire in parallel and series, a simple search on the web will likely yield plenty of examples, try "how to wire resistors in series and parallel")
To check your math in parallel resistors, the total resistance will actually be smaller than either R1 or R2. So, we want to put our resistors in parallel, to lower the high resistance of the LED bulb so that the current draw on the circuit overall is higher (like the original bulb). I found that 6Ohm load resistors were relatively common on the interwebs, so lets use that.
R1 = LED fixture resistor
R2 = Load resistor [6Ohms]

(104.3 * 6) / (104.3 + 6) = 5.67 Ohms

now back to the top equations
Current = Voltage / Resistance
or 12V / 5.67 Ohms = 2.11A

Now we see that we are just slightly higher than the original bulb, so this will let your car's turn signals operate normally. Now, it is important to note here, that if you wire your load resistor in series, you will have a combined resistance of ~110.3, which will NOT solve your problem. the current would still be very low and your car would still think the bulb was burned out.


Is there an alternative to load resistors?
maybe. the turn signals are controlled by several different methods or control cirucits, and in some cases, there are methods of modifying these control circuits to just accept the lower current draw of LEDs. The control methods vary greatly by year and make of your vehicle so there may not always be a solution. In some cars, they use flashers, which can be replaced to allow for lower resistance. A flasher is basically a relay and the control circuitry in one module. Some cars have a relay, which some people may say to replace, however a relay, by definition is just a contractor or automatic switch. it receives a signal from the actual control unit, and closes allowing current to pass through, which lets your signal lights light up. I can not advise you on how to modify your own control circuit, since they would all likely be very different. And if you are lucky like me, and have an 09 Lancer GTS or similar, the control circuitry is inconveniently located within the same module as the cars central processor.. Which means removing it and modifying it is tricky, time consuming, and if you mess up, a replacement is about $600 plus the cost of re-flashing (reprogramming) the Processor. So the best option is probably the load resistor route.

For LED lighting products including load resistors, I highly recommend http://www.superbrightleds.com/.

I have had lots of their LEDs all over my car for over 2 Years in Chicago weather, so 100deg heat and 0 deg cold, and they are all still functioning great. I also like, being the nerd that I am, that they provide full specifications on all the replacement bulbs they sell, so I can do all the calculations that I have provided above. Surprisingly I am not a spokesperson for them, I just like their products. I will say they are a bit pricey, but you get what you pay for, right?

Well, this concludes my lecture on Load resistors, I hope that those of you that had the attention span to read this post, and did not fall asleep found this to be helpful, if not verbose. My qualifications for writing this post are that I am an employed Electrical Engineer in Chicago, and that I own a 2009 Mitsubishi Lancer GTS. I can site sources upon request for any of the aforementioned information. Best of luck to all of my fellow modders!

 

Awesome write up Engin3rd! Mods - info like this should be stickied!!

 

Wow, Thanks so much for explaining that. It reminds me of high school physics haha. It makes so much more sense why I need resistors!

 

So I purchased Altezza smoke LED tail lights to replace the stock lights on the rear of my 09 GTS... everything works fine EXCEPT for the red brake lights that are on the trunk of the car, they don't light up... my turn signals, brake lights on the outside section of the tail light and the reverse lights are all functioning... I did note that the brake lights on the trunk section are a smaller bulb and after reading the awesome sticky on resistors i'm now thinking that maybe I need a resistor for this connection but am not sure...

Has anyone else installed Altezza LED tail lights and have had the same issue? any suggestions on what might be the issue and whether I actually need resisitors or not?

 

Actually, I don't know about that. It sounds like you may have just gotten a bad pair, or that something is not making a good connection in that section of the light.. Just to clarify the simplest of possibilities, you know that the tail lights on the trunk do not come on with breaks, and only function when you turn the headlights on? so if you turn on the lights in your vehicle, they should be on, if they do not come on in this situation, it is possible that the plug leading to them is not seated correctly. (the plug is not making a proper connection). so try unplugging them and then plugging them in again. but if your original tail lights in that area functioned correctly, then the only likely explanation is that something is not correct inside the new tail light. If this is the case, I would suggest using the RMA process if available, for faulty merchandise. If no warranty or return policy is available, you may be able to repair them yourself, with a bit of luck that the problem would be visible or easily identifiable. But, lets first rule out the possibility of a faulty connection at the plug, or that you simply hadn't turned them on yet. Please try turning on your headlights, and see if that works. next try reseating the plug, and see if that works. and finally, try putting in your old bulb into that plug and verify that it works as it originally did. then please report back with findings. Best of luck.