I confirmed that is how I originally wired it. The amp is powered only when the car is in "Ready" mode. I finally got around to installing a 2 farad capacitor next to the amp. I took some measurements to see if it was worth the time, effort, and money. To minimize risk of damage to the DC system, I turned off all other power draws before setting volumes on the head unit, processor and amps to near maximum. Using track 14 of the XLO/Reference Test & Burn In CD (a Big Band tune that blasts a very wide swath of the audio spectrum), I measured peak amperage and maximum voltage drop on the line feeding the amp. Highest amperage reached was an instantaneous 64.0A, with an accompanying max voltage drop of 0.9V (from 14.4 to 13.5). That's a 6.25% drop using a capacitor double the recommended size for a 900W amp (in this case only pumping out about 690W: 13.5V x 64A x 80% efficiency) . So yes, a capacitor is definitely in order for operating a system like this at a near maximum volume level in order to protect the DC supply system. Done. I have a PLX Kiwi ODB2 feeding the Torque application on my Android phone. It is unecessary, though. See last part of the reply below. My guess is that your reading mostly took place on DIYMA. Every online community has its own unique culture. Priuschat participants seem to value efficiency. DIYMA folks seem to dislike capacitors. Perhaps it is the nature of the vast majority of batteries used to power thier equipment (large, cranking batteries specifically designed to power large amperage draws for short periods), or that many of them like to listen to their systems for extended periods of time with the gasoline engine off, and want the additional listening time. A Plug-In Prius is a different animal. It does not even have a cranking battery, but does have a massive additional battery already that could provide power (in "Ready" mode) much longer than any single additional battery solution they might come up with. If ever there were a car that would benefit from a capacitor, it is the Plug-In Prius. All that said, this capacitor experiment was an academic excercise. I never before, nor ever will again play anything in this car at anything close to this sound level. In order to get near the car while it was playing at this level, I wore foam inner-ear plugs, and mickey-mouse earphones over the top of the ears in order to protect my hearing from damage - and it was still very loud. After attenuating the volume to the loudest I would ever consider listening on the JBL processor master volume (-20dB), I added 5dB for a little leeway, and measured the same sample audio again. The result? 6.0A peak and a max voltage drop of 0.05V, less than 0.4%. At this power draw, I probably do not need a capacitor at all. Another lesson learned - 6 amps is less than 70 watts total being fed to all of the speakers, including the subwoofer, so it also tells me a lot about how much power I really need. If I had it all to do over again, I would power the 6 speakers directly from the JBL MS-8 speaker outputs (20W ea), and use a single 100W to 300W amp for the sub.