what resistor will i need?

[peanotation]

project: i want to have my third brake light on my spoiler always on when the parking lights are on, but i want it to be just as dim as the tails. then when i press the brake, the 3rd brakelight on the spoiler will light up to it's fullest brightness, which is equally as bright as my tails.

i already figured out how i'm gonna do it with a relay, but my question is, what resistor will i need to make the 3rd brake light dimmer? i went to radio shack and i just got overwhelmed by all the different ohms and different wattage on them. i dont care if i have to buy like 10 different ones to make it work, does anyone have a ballpark range for me to stay in? thanks

[pinoyesv6]

why don't you buy some pot.

you know, a potentiometer. its a variable resistor. you turn the knob to control the brightness of the light

[Livn2sk8]

Off topic, but not really, what could I solder in, to make my 3rd brake light, blink/flash, you know? slowly? like some of the new cars have???

[peanotation]

<div class='quotetop'>QUOTE(Livn2sk8)</div><div class='quotemain'>Off topic, but not really, what could I solder in, to make my 3rd brake light, blink/flash, you know? slowly? like some of the new cars have???</div>

there are things that do that at radioshack, i forget how much they are, but i remember them not being expensive at all, i know i've seen 'em though. out of curiosity, why would you want that?

and thanks about the potentiometer, i'll be getting one tommorow.

[JiP]

Wait..Your tails are always on, and get brighter when you hit the brake right??

I dont really remember the setup but I dont think a second bulb comes on when you hit the brakes, just the 1 bulb there gets brighter right???

If thats the case just wire the 3rd light up to the left or right tail light power wires.

Otherwise..If your 3rd brake is LED then you will most likely need only 1/4watt resistor (the tiny brown ones) but the actual value of the resistor is kinda impossible to determin based on light intensity. Your gona have to wire up a variable resistor (potieniometer) turn the knob till you find the intensity you want, and either glue the knob in place so it dont turn or get a volt meter and measure the resistance, and go buy a standard resistor that is close to the same value and wire that in.

No real reason to buy the resistor to replace the variable one other then to save space.

[peanotation]

<div class='quotetop'>QUOTE(JiP)</div><div class='quotemain'>Wait..Your tails are always on, and get brighter when you hit the brake right??

I dont really remember the setup but I dont think a second bulb comes on when you hit the brakes, just the 1 bulb there gets brighter right???

If thats the case just wire the 3rd light up to the left or right tail light power wires. Â* </div>

no, i mean, when my tails are on (i.e. driving at night) i want hte 3rd brake light to match the intensity of the tails. then when i press the brake, i'll have the relay throw to the other side and just send a direct current through, which will light up the 3rd brake light completely. normal day driving, the 3rd brake light will be off, cause the parking lights are off, and when i brake it'll light up full brigthness.

the 3rd brake light, cause it's on my spoiler, is a row of tiny LEDs. i'm just gonna get the potentionometer and keep going till it matches the tails. then i'm just gonna wrap it in tape 1000 times and shove it in one of the little holes on the top of our trunk

[know_fun]

u need to find the formulas for changing from a 12volt to a whatever watt led (basically the resistor is to restrict power of the battery to the led). sorry i forgot all my formulas hope this helps though

[pinoyesv6]

he doesn't need the forumla for the LED's since the LED's already have the 12v input on them. he just needs to add a resistor somewhere because he wants them to be dimmer. i suggested to use the pot because we don't know how dim his rear taillights are and a pot would be the easiest way to change the brightness on his spoiler light to match his other lights perfectly.

[Radnoken]

<div class='quotetop'>QUOTE(pinoyesv6)</div><div class='quotemain'>he doesn't need the forumla for the LED's since the LED's already have the 12v input on them. he just needs to add a resistor somewhere because he wants them to be dimmer. i suggested to use the pot because we don't know how dim his rear taillights are and a pot would be the easiest way to change the brightness on his spoiler light to match his other lights perfectly.</div>

Yeah what he said. A POT is the only way you can go to get the look you want. And in case you dont know a POT is just an "adjustable" resistor.

EDIT: Just fixed some spelling above. :oops:

[tolowbass]

ummmmmmmmmm POT....... ill be back in a few.... after my nap

[JiP]

most LEDS will blow with direct 12v, but the ones in the 3rd light are definitly setup already just to hook to 12v.

Dont think there are no formulas to change voltage to light intensity.

And what you want to do is what the car already does to keep the tails on and get brighter when you hit the brake. 90% sure I just havnt looked at the schems yet cause im too lazy..

[Radnoken]

Hmmm.... led's already hooked up to tail lights.... now i've got to go see what my lights are doing.

[peanotation]

i dont think you guys are understanding me. my OEM third brake light is disconected, because my Evo VI wing has a third brake that is a row of LEDs behind a red lense. the ONLY connection the spoiler third brake light has is just two tiny wires, one ground, one 12v. If you hook it up to a 12v source it lights up to fullest capacity, full brigthness. Right now it's just a brake light, i re-routed the OEM third brake light wires to the spoiler.

I want it to be on at 50% intensity, lets say, when the tail/parking lights are on. And when I press the brake, the relay will throw to the other pole and direct a 12v constant un-interupted stream of power to the third brake light. I'm gonna go out and get the potentiometer, but there's like 10 different ones at radio shack. Different wattages. Different ohm loads. I'll probably buy 2 of them. I know not to get an audio one, cause it's an exponential increase of power, whereas the linear ones are just a 1:1 ratio of power increase as you turn the knob.

[JiP]

Your the one not listening!! =P

I looked at the schems the tail lights have 2 bulbs 1 is on when you turn the lights on hitting the brake turns both on and makes it brighter.

So ye you will need your relay setup, and A VARIABLE RESISTOR!

[peanotation]

yeah, i know how i'm going to do it. i'm just going to be tapping into the parking lights and then the brake lights. i still don't know which potentionometer to get.

[JiP]

you dont have to tap the brake lights....if you design the circuit correctly =P

im not in radio shack so I cant see your choices.. and I dont know how many amps your 3rd light pulls at full brightness...but id guess a 10k pot will be plenty to give you room to adjust, and as far as size well you dont want a very very tiny one because it wont handle too much current, and you dont need a huge one with a long shaft (i knwo RS sells that kind)..

[peanotation]

<div class='quotetop'>QUOTE(JiP)</div><div class='quotemain'>you dont have to tap the brake lights....if you design the circuit correctly =P</div>

well, since i have the connector from my OEM brake light just dangling there, i was gonna have that be the power source for the brake light on the spoiler. i was just gonna tap into one of the tails for the tail light.

[JiP]

Have the brake light power trigger the relay to switch from sending out power with the resistor on the line to sending out a straight 12v signal.

[Reelax]

Off topic, but not really, what could I solder in, to make my 3rd brake light, blink/flash, you know? slowly? like some of the new cars have???

http://autolumination.com/dcell3.html

[RedGalant2k1]

Well if you want learn what each different color stripe for each different resistor means go here: www.the12volt.com it has a FAQ section that describes the entire array of resistor combonations, plus much more.