Your LEDs are "typically" 3.3V. They might be 3.0V (then will have too much current if you use your 39 ohm current-limiting resistor) or they might be 3.6V and be dim with your resistor. That is why a current source circuit is used.

I don't know your LEDs. Their mounting base might need to be electrically insulated but still must pass heat which cannot be done with silicone.
A heatsink is usually aluminum which conducts heat much better than steel.

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Uncle $crooge

 

The resistor is dissipating E^2/R=1.25*1.25/4.3=0.39W so a 1/2W resistor is more common and cheaper.

C1 has to be purchased (look here).

When mounting the LM317 (TO220 package), it cannot short to the car frame. I would screw it to the car body using a nylon screw, with an insulating mica washer between it and the car metal. That way, no heatsink is required.
btw- reading some of the previous posts, only the heat produced by the regulator itself and the power dissipated in the resistor is conducted to the "heatsink". That power is ~1W in the regulator and ~0.4W in the resistor for a total of 1.4W.
OTOH, each LED is mounted someplace else, and it dissipates 3.3*0.3 or about 1W, so Carl is right, you will need to devise a mounting for each LED which mounts it mechanically, but conducts heat out of it to the car body.

The resistor can go either way around and be soldered directly between the Vout and Vadj pins.

The capacitor I show above is not polarized, and one lead should be soldered to Vin and the other grounded to the car body near the regulator.

The LEDs are polarized; one lead is called anode, and the other is cathode. The string of three LEDs is wired anode of 1 to Vadj;
cathode of 1 to anode of 2;
cathode of 2 to anode of 3;
cathode of 3 to car body. If you are mounting the three LEDs in different locations, you will have to daisy-chain a wire as needed.

Power feed wire to Vin. Connect other end to fused connection in the car's fuse block. 1A fuse is sufficient.

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This is extremely helpful, I appreciate you took the time to draw a diagram I completely understand.

A nylon washer as you are saying, will conduct heat connected to the car chassis, however it obviously will not conduct electricity the resistance is far too high right?

As for the LED's, I dont think they come with the star base, so I realize I cant just mount them to the chassis then either that would ground them, but I can use some sort of thermal silicone or compound to put onto the chassis? Or is that resistance low enough to short the LED out also?

Thanks again you are all very helpful

Edit: Now that I looked back, could I just use this for the LED to mount to the chassis? http://search.digikey.com/scripts/Dk...&name=4651K-ND

And then epoxy it around the outside to hold it on?

 

The LED mounting has to hold it mechanically, isolate it electrically, but conduct heat to the underlying car body metal. For 1W of dissipation, bonding it to painted car metal with a thin layer of 5min epoxy may be sufficient, as long as you test each one for a short to ground after the epoxy sets up.

 

How would I test this, without damaging the LED's?

 

Ohmmeter (Multimeter set up to measure Ohms)

 

Ok, and im guessing 0 ohms would mean that it is shorted, right?

 

Right. The reading should be >10megΩ, or ∞ Test both anode and cathode to car body.

 

There's only one sane way of powering high power LEDs are far as I'm concerned: with a switching regulator. It doesn't have to be anything complicated, just a 555, a MOSFET, inductor and diode will do in most cases.

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I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.