Hi,
The 1000uF capacitor was added as I was following the Neopixel uberguide best practices.
Before connecting NeoPixels to any large power source (DC “wall wart” or even a large battery), add acapacitor
(1000 µF, 6.3V or higher) across the + and – terminals as shown above. The capacitor buffers sudden changes in
the current drawn by the strip
I also added the 220uF closer to the strips as the 1000uF is situated about 3m of wire away.
They go off almost immediately when the power is first turned on. After the engine as run hard for around 20 minutes, they stay on for much longer, and you can definitely notice them fading to red before they turn off. It is like there is suddenly more capacitance, or the capacitors are draining much more slowly.
I did toy with the idea of using a linear regulator, but I didn't like how hot it got dissipating the extra voltage as heat. I am already having a problem with heat, I don't need anymore.
The buck converter is a cheap eBay variety. Very similar to this: eBay Link