Using 12v car battery to supply multiple "3.5v" devices
Your reading of 430 ohms does not reflect the current limit of the supply, although I don't know exactly what it does show. 

Assuming 3.2 volts per LED at 0.45 amps, if your battery really is a 12 volt battery at that current (which I doubt), 







simulate this circuit &ndash; Schematic created using CircuitLab
will work - maybe. The 3 LEDs are in series, so they all have the same current. Assuming 3.2 volts for the LEDs, and 12 volts for the battery, this leaves $$V_R = 12 - 9.6 = 2.4 \text{ volts}$$ Then, in order to get a current of 0.45 amps, $$R = \frac{V}{i} = \frac{2.4}{0.45} = 5.33 \text{ ohms}$$

The reason I say "maybe" is that batteries don't usually have exactly the stated voltage, and it varies with both load current and state of charge. I'd suggest starting out with a 10 ohm resistor and get a feel for the circuit.

Oh yes, and you'll need a decent power rating on the dropping resistor. The power dissipated will be the voltage times the current, and I leave that for you to calculate. But it will certainly be more than 1/4 watt.