Before I wired in numberous 12V devices I had to install a 24V to 12V converter.  I used this Sure Power Industries model which was about $200 USD and provides 17 amps of power which is more than enough to power everything I want other than off-road lights.  I installed the converter under the hood and it can be seen in the right side of this picture.  I currently run my 12V in-dash CD player, all gauges, AC system, and have converted my cigarette lighter as well to 12V.  It has a memory function that also allows 12V items with clocks, like my CD player, to continue to keep time.  Likewise, my CD player uses the ignition activated setup to draw the majority of it's power (7 amps?) from the converter's constant 12V supply.

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