[brucepick]

First off, yes, it was a problem on my '97 Civic. Restarting the engine caused the radio to shut down and reboot. The problem was worse when listening to CDs or when listening to any spoken material - if you miss a couple words you can lose the whole thought.

Another project provided insight into what was happening. I installed TWO deep cycle batteries in the trunk and deleted the underhood battery. I installed a new stereo and had the option of powering it from whichever battery I chose.

One battery powers the starter motor and headlights. The other powers everything else, including (currently) the STEREO. This works well. Key-starting the engine does NOT reboot the stereo. However when I wired the stereo to run off the battery that powers the starter, key-starting the engine DID cause the stereo to reboot.

So I deduced -
Nothing in the car's logic circuitry cuts power to the stereo when keying the engine. However, the voltage drop of starting the engine does cause the stereo to cut out and reboot.

Note - this installation has both positive wires for the stereo powered by the same battery. There is some possibility that by running these two leads off different batteries one could also avoid engine-start stereo shutoff, but I didn't take the time to test the various possible combinations.

Modern car stereos have one positive "constant power" lead which keeps the clock and memory going, and also provides the necessary current for its other electronics. The other positive lead could be called an "enabler". It is switched on/off by the ignition switch. The stereo will run or can be turned on only if that lead has power, but it really only permits the stereo to run, doesn't provide a significant amount of power. I didn't take the time to wire the two leads to separate batteries to see what would happen.