I read a thread recently about the importance of using resistors when installing LED lights. Well, recently i had an auto electric shop install some blue led side-mirror turn signals i bot on ebay, and i know they didn't use any resistors; they just spliced into the existing turn-signal wires. Last night, i installed two blue led license plate screws by splicing into the existing rear license plate light wires. I also installed some amber side markers (normal bulbs) by splicing into the same wires that were used to hook up the blue led turn signals. My next project is to add four blue leds to light the floor of the cab, two lights on each side, when my headlights are on.
Questions: do you see any potential problems with the way i have my lights hooked up? Regarding the four leds i'll be installing, under the dash, what color is the wire to the headlights, and what, if any resistors should i use? Should i connect the four leds in series or parallel? Thanx very much for your input, as i don't know jack about electric wiring.

 

If you install LED turn signals without resistors, hyper flash will occur, as the LED's draw less voltage/current and the safety systems on the car thinks a bulb is burned out. I am not familiar with using resistors for any other LED lighting application.. such as you describe.

 

ok; lets see. as for the sidemirror and license plate() LEDs. they would have come with the resistors prewired in their system to accept 14.4volts. if they didnt, 1. they suck, and 2, they would have blown out instantly.

now. the blue LED turn signals should get a hyper flash, but not anything to do with the resistors. not exactly. they too use resistors to drop the current but they dont actually draw any; which still throws the system checker off. then there are huge resistors in the 10-20w range that can simulate a functioning bulb and fool it into thinking there is a bulb there; and no hyperflash.

you adding the regular bulb sidemarkers might have actually done the job to stop the hyperflash. depending if you spliced it in series or parralel(should be parallel I beleive)

anyway; your question. regular old LEDs like 5mm not presetup or anything... they need resistors to drop the 14.4v that cars have down to what they need... in your case 2 blues per side; setup 2 in series; blue being 3volts. on average. need a 430ohm resistor. but that depends if the LEDs you get are actually 3volts; and run 2 to a series.

if all that went over your head; let the shop do it. you can only really 3 in series ideally. so running 2 and 2 is best.

this assumes regular LEDs too. if you buy them premade in some form(seen a few overpriced stuff on ebay) they might be pre setup for use in a car to run individually off 14.4volts.

 

Ok, ares, why the frown? I like blue, and i like shiney things; i am also an excellent driver .
What the heck is hyperflash? It sounds cool, like something teknosquare should be doing .
What i have noticed with the led turn signals, which i have had installed for about two weeks, is that the bottoms of the signals now have a sl. brown tint (burned?) in the plastic covering, but the signals still work fine. Is this hyperflash? Another thing i noticed is that when i first used my signals with the leds hooked up, i heard a high-pitched backround noise with each "blink". I then disconnected the battery for about 5 minutes, and when i reconnected it, the noise went away.
All the lights i am describing were bot on ebay motors, and all were advertised as being designed for automobile applications, so maybe they do have internal resistors cuz they didn't burn out.
In series would be end-to-end, right? What i have done is kind of like grafting a new branch on a tree--i just cut away a bit of the live wire's covering and "grafted" the wire of the led onto that part. This is in parallel, isn't it? See what an electrical moron i am?
About the 4 under-dash ones i'm gonna install to light the floor when my headlights are on, what color is the headlight wire i need to splice into? Is there a seperate wire for the right and left headlights under the dash? If so, what color are those two wires? I guess i'll have to run two leds off of each wire, or am i way off here?

 

hmmm.

hyperflash is where the turn signals flash rapidly. twice as fast as ussual. the car does this to signal that a bulb is burnt out. it isnt sensitive enough to notice the tiny amount of a current that an LED should use.

Im a bit curious what you did buy though, for one; any LED will get hyperflash. it is not possible to fit the nescessary resistor to counter it inside the bulb; it is wired outside on the wires going to the bulb. youd know if you put something like this on. next question is; LEDs should be cool. furthermore; stock bulbs hit over 200degrees; at which an LED would be toast in seconds. but the brown color you describe is ussually from excessive heat. something here does not sound right.

there should not have been any noise from it either.

series is end to end; for the stuff you wired; it would be that you spliced in on the positive lead; and again on the negative. series would be if you cut one of the lines and connected them through the new addition. sounds like you did parralel which is correct.

for the underdash; you do want them end to end. in series. headlight wires probably dont get into the cabin. the fuse is by the battery I beleive; and the switch in the cabin probably goes to a relay. so youd have to feed a new power lead through the firewall for it. only need one and put the 2 series of 2LEDs in parralel off that 1 power lead. you can then find a ground anywhere.

I dont know any of the colors off hand.

 

guess you didn't get my obscure "rainman" reference.
My signals currently flash at about 1 blink/sec.
There must be headlight wires in the cab, running from the switch at the steering column, right? I was planning to splice into that wire to supply juice to the underdash leds.
Wouldn't it be great if there was a place on the web where one could go to find the color schemes of the many wires we have in our car? Some wires, like the turn signal ones, actually change color depending on where they are located in the car, which sux greatly. Do you know of any such place? I need to find the color of the headlight switch wire in the cabin.
I'm gonna attach pix of my led and amber turn signal setup:

 

A better one of the side-mirror led:

 

my guess is the switch in the cabin is just to complete a ground circuit that trips a relay under the hood. I dont think that high of a current draw would go through the switch; so in that case it probably doesnt come anywhere near it.

 

Why would that be true for the headlight switch wiring but not the turn signal switch wiring, from which i have been able to draw enough current to light both the new blue led and amber side markers?

 

you tapped into those under the hood and by the front bumper, didnt you? being that both are near those locations; I wouldnt imagine youd go into the cabin for it.

but I cant say for sure; cause I really havent followed the wire back or anything. just speculation; typicly you dont run a high current line any farther than you need to; increases the risk of a short.

 

you tapped into those under the hood and by the front bumper, didnt you? being that both are near those locations; I wouldnt imagine youd go into the cabin for it.

but I cant say for sure; cause I really havent followed the wire back or anything. just speculation; typicly you dont run a high current line any farther than you need to; increases the risk of a short.

 

Well, the auto-electric shop that installed the side-mirror leds tapped into the turn-signal wire in the cabin under the dash, so when i installed the amber side markers, i did the same.

 

As for LEDs... a few have built-in resistor for 12V operation. One example are those windshield wiper LEDs. Hooking up a regular LED without a resistor is like lighting up a small firecracker. It stinks... literally. :-)

 

Well there you have it...mine obviously have resistors, cuz it hasn't exploded, and it doesn't stink;-)