Step 18: Secondary light sources - Installing
For your array layout (in my case, 12 chains of 9), plan the best way to wire up your chains. Then, carefully solder each LED in a chain together, from the shorter negative lead of the previous LED to the longer positive lead of the next. At the ends of each chain, there should be a clearly indicated red (positive) and black (negative) end, and ideally have some sort of keyed connector back to the junction board to make life easier.
At this stage, you should test your LED chains to make sure all the LEDs work, and are connected the right way around. *cough* Ease of access is one reason it is better to wire in the secondary light sources before you put the optical fibers through. The other reason is that optic fibers are made of thin filaments of plastic, and tend to melt right through at the slightest touch from a soldering iron, so keep them well apart from one another.
Once everything is working, apply some wood glue around the outside of each LED assembly to keep them in place, and make the connections neat