acc to start = radio power cycles

I think what I want to do might be impossible, but maybe some of you geniuses have an idea. I have a 95 Subaru Legacy outback Wagon and an Alpine HD138BT. If I go to get gas and put the car from start to acc, the radio stays on without a hitch. Once I'm done filling up and I go to start the engine again, the radio flashes off and then back on. I'm wondering if there is a way to eliminate this issue. I feel like this is just a feature of the HU and I can't really do anything about it. I was also wondering if there was a way to keep the radio on until I close + Lock my doors. Just to get every last bit of whatever song was playing on there. About that I should probably let you know that I have a Viper 5101 Alarm/Remote start/ keyless entry system wired up. My car is a manual but the remote start is in automatic mode thanks to someone's ingenius magnetic reed switch design.

And setting the R/S to to RAP (retained ACC power) if it has that feature won't help. It dumps as soon as you open the door. Nope the reason is ALL circuits on the ignition bar ign. 1 and start are dumped during cranking to save your battery. The Alpine's red lead could be rewired as a constant but then you might forget to turn it off draining your battery. You could try a 5 minute timer triggered by your ignition wire going to neg when you turn off slowly, that might work. BTW it doesn't take a genius to know that all Suburus of that vintage have a neutral safety from the gearbox to the engine management hence "someone's ingenious reed switch design" was totally unnecessary as was calling a reed switch relay magnetic because by definition reed switches are magnetic.

If it's like my Alpine CDE121 and others I've had, you'll need a dc-dc converter OR a dual battery setup OR a lower voltage drop (ie, reduction starter or a bigger battery or lower resistance battery etc). The Alpines do cut out on voltage sags. I'm not sure what the threshold voltage is, or if it's in response to a certain rate of voltage drop. Both my Alpine constant and IGN +12V power is from the battery (and always has been, though with the CDE121 with its ~100mA drain, the IGN +12V is now relay switched).

I actually have a whole system in my car. The battery in front of the car is hooked up to a optima yellowtop in the trunk. Oldspark, I think you are talking about the head unit shutting down because the battery doesn't supply enough power? If so, that's not my issue. I am an idiot, thanks, I think your post has the solution to my HU shutting off on engine crank. So it looks like if I add in a 1N400x and a 470 microfarad capacitor inbetween my ACC 12v constant wire and the 12v constant wire of the head unit, I should be mint? I think the capacitor will power the Head unit for a few seconds which is just long enough for it to withstand the power drop when the engine cranks?

It will probably take upwards of 4700 mic worth of capacitance. And a 3 amp diode. Or parallel 3 1n400X.

Why not power the HU off the 2nd battery?

What's the point of this post? I've had Alpine units since the late 70s and shutting down for the 1/2 second whilst the key is being turned never bothered me.

I am guessing he is trying to keep a bluetooth call connected.

"I am guessing he is trying to keep a Bluetooth call connected". No read his first post:- "Just to get every last bit of whatever song was playing on there"; hence my comment. And you Craig with your vast technical and practical knowledge should know better; If he's started a call through the BT, it will stay connected even though power has been removed from the ACC until the call has ended.