Convince yourself to just use a 12V-to-AC-line inverter for LED light strings instead of rewiring them for 12V.

Step 2 Figure out how to split up the string.

The string I have is 60 LED's long. I wanted to minimize the amount of time I spent on the project so I figured I would just take them in order and add a current-limiting resistor to each mini-string that would drop the 12-volt input to whatever is needed by the LED's. The original string had a sequence that went green, blue, red, orange, yellow.

And from the last step, the voltages for each LED were:

Blue: 3.0V
Green: 3.2V
Orange: 2.0V
Red: 5.2V
Yellow: 2.0V

So now we start at green (3.2V) and add orange (2.0V for 5.2V total) then red (5.2V for 11.4V) and that's it because adding yellow (2.0V) pushes the total to 13.4V which is more than the 12V input voltage. Here's a chart of what happens:

Color   Voltage Total
Green   3.2     3.2
Blue    3       6.2
Red     5.2     11.4

Orange  2       2
Yellow  2       4
Green   3.2     7.2
Blue    3       10.2

Red     5.2     5.2
Orange  2       7.2
Yellow  2       9.2

This works out quite well because now the sequence is once again back to green where we started! Now it's a matter of figuring out the resistors. For instance, in the first string, there's 0.6 more volts to reach 12V so that's what the resistor will have to drop. Using Ohm's law, that's 0.6V / 30mA = 0.6V / 0.03A = 20 ohms. The rest of the resistors are as follows:

Sequence  Voltage  For 12V  Resistor
G-B-R     11.4V    0.6V     20 ohms
O-Y-G-B   10.2V    1.8V     60 ohms
R-O-Y     9.2V     2.8V     93 ohms

So there's 60 LED's total and the three sequences contain a total of 10 LED's each so that's 6 sets of sequences. Or 18 sequences -- each that need to be soldered up.

Ugh ... am I even on the right track?