Stopped at radio shack and bought some LED's to be used as turn signal and brights indicators.The guy says I have to solder resistors on and then solder the wire on. Is this right? I feel like a fire waiting to happen........got to be a better way.

Kevin

YES, That's right. If you don't they'll be toast in a second.. I think mayabe a 1000 OHm resistor would be right.. And if you hook them up backwards, you get nothing...

The LED is the current limiting device in the circuit, the resistor will not create a fire hazard.
I use LED's for that purpose without resistors.
Are they 12 volt and the resistor is there to protect against 15v?

But how do you keep it from shorting or grounding out? Shrink wrap? Do they make it that small?

The guy asked how many volts and I said 12. Wasn't thinking about it can get up over 14.

The resistors go in front of the LED and keep it from frying.

I was thinking fire due to the bare wire coming from the LED and resistor.

You need to find an electronics supplier, someone like Mouser, to buy LED's from Some LED's come with built in resistance for 12V operation, others do not. LED's will self destruct if you don't have a resistance in series--and again--some are built in. Even if you wire enough in series to "handle" say, 14V, and your regulator takes a momentary nap, a slight surge might blow one or more of the chain.

THe way LED's work, is that they ARE a diode, and light when "forward biased"--they are CONDUCTING, and this means for simple purposes that they are nearly a dead short when turned on. There is nothing in a diode / LED itself under this condition to protect from catastrophic high--current failure

On the package you bought will be two numbers. One will be a voltage (drop), and another will be a rated current.

For example, if the voltage is 3v, and current is 20mA, you need to find a resistor to get that current.

So, 12v - 3v = 9v across the resistor
9v/20mA = 450ohm, 1/4w resistor in series

Solder it all up and cover it hot glue to keep from shorting

If you post the actual numbers I can figure out the resistor you'll need.

-Dave

The LEDS you got from RS are rated at 3.6 volts. I used them lately on some RC helicopters and used a 220 OHM risister with a 7.2 volt Lipo battery.

450-500 Ohm sounds about right with 14 volts.

You may have trouble locating a 450ohm ¼ watt resisters, I have used 470ohm resisters from Radio Shack for this purpose for years in automotive applications. Yes shrink tubing is available in very small sizes and is the best choice to insulate the leads, pricing is not the best but Radio Shack has them as well. As mentioned, most LEDs need to be limited to about 3.3volts/25ma. Here is a LED array put together to replace the dash mounted map light in my current project. There are three paralleled strings of four LEDs in series. No resisters required as there is no more than 3-3.5 volts and 25ma across any one of them. Very bright white light and no plastic melting heat, pulling about 75ma total current.

Yep, I forgot to mention that you'd need to find a resistor close to that. Also should account for 14-15v, rather than 12v.

-Dave

The green LED is (5mm) 2.1 volt-30 mA 630 mcd with a 330 ohm resistor 1/2 watt 5 tolerance.

The blue LED is (5mm) 3.7 volt-20 mA 2600 mcd
with a 470 ohm resistor 1/2 watt 5% tolerance.

excuse my ignorance but why not just buy automotive led bulbs?

wouldnt that be easier? thats all i did.

Two reasons, as many automotive LED replacement bulbs there are available today there are just as many bulb types used in these old cars that don’t have a direct LED substitute, especially the small indicator type bulbs. In my map light case very little depth for any premade LED lighting.
Secondly, As overpriced Radio Shack is for their small parts, it’s cheap compared to some of those automotive LED replacements I’ve seen.

If yu purchase the Painless Wiring LED's from Summit or Jeg's, they do not require a resistor. I even spoke to them directly and installed it. No resistor required for painless' ..

No ignorance to excuse. I thought what I was picking up at RS would be automotive, but I had never seen them before and when he laid them out on the counter I asked," Are you sure there is not a better way?". He said "This is it."

I'm not the sharpest tool in the shed, but I knew something wasn't right.

These are not replacements. I'm making an insert for a 68 Cuda dash I'm putting in a 67 Dart.

I need the LED's with insulated wires out the back and holders to mount them in the panel.

808cuda, I tried Summit and had no luck searching for LED's. Would you have a part number?

i used these guys before look nice and super easy to install.

http://www.designengineering.com/products.asp?m=sc&cid=5


Any speed shop can get them for you or maybe jegs or summit

when i did my dash i bought 194 blubs that were LED's. that was ok but pretty dim.
so early moring ebay hunting i found prewired led's that i soldered onto my pc board and did it that way. they are superbright and no problems seeing the gauges now. .

kinda like these ones.

led's

I've bought a bunch of stuff here:
http://www.superbrightleds.com/

Plan to spend 15-30 min browsing their site and seeing what your options are!!!