Use just a capacitor to keep your car (or truck) stereo on - when your ignition switches off the ACC power - while starting your engine. One 16 volt 3300 uf cap sustained the power for about 2 seconds to the ACC . I installed two to get about 4 seconds of power.
The ACC wire wouldn't charge or pass thru the cap to the stereo, but the "always on" power supply did. So I wired the cap from the constant power to the (already connected) ACC line. I thought this would keep the radio on all the time, but it doesn't. When I take the key out, the radio stays on for a few seconds then shuts off.
Exactly what I wanted.
UPDATE 1: At the end of the video I showed adding a USB charging port. If I am charging my phone when I turn the key... the phone takes the voltage stored in the Cap and the stereo does NOT stay on. (boo!). So I have to unplug my phone when starting the car, or wait to plug it in.
UPDATE 2: I later added a subwoofer/amp. I currently have it powered from the same wires shown in the video. That drains the cap as well (even without a phone charging). I'm committed to getting this wired right... but it may be a few weeks before I can. I may just add a toggle switch in the center hole (don't tell my wife). A capacitive touch switch may be in the works as well (so I can hide it).
UPDATE 3: So... yes. I did this wrong. It kinda worked so I thought it was ok. I re-did it with:
1. Negative of capacitor to ground
2. ACC power from vehicle to Positive of capacitor - then to the stereo.
It later found this guy who has the same stereo and did the hack correctly... watch his video too.
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